ROOT   6.10/09 Reference Guide
ROOT::Experimental::TDataFrame Class Reference

ROOT's TDataFrame offers a high level interface for analyses of data stored in TTrees.

In addition, multi-threading and other low-level optimisations allow users to exploit all the resources available on their machines completely transparently.

In a nutshell:

ROOT::EnableImplicitMT(); // Tell ROOT you want to go parallel
ROOT::Experimental::TDataFrame d("myTree", file); // Interface to TTree and TChain
auto myHisto = d.Histo1D("Branch_A"); // This happens in parallel!
myHisto->Draw();

Calculations are expressed in terms of a type-safe functional chain of actions and transformations, TDataFrame takes care of their execution. The implementation automatically puts in place several low level optimisations such as multi-thread parallelisation and caching. The namespace containing the TDataFrame is ROOT::Experimental. This signals the fact that the interfaces may evolve in time.

## Introduction

A pipeline of operations is described to be performed on the data, the framework takes care of the management of the loop over entries as well as low-level details such as I/O and parallelisation. TDataFrame provides an interface to perform most common operations required by ROOT analyses; at the same time, the users are not limited to those common operations: building blocks to trigger custom calculations are available too.

TDataFrame is built with a modular and flexible workflow in mind, summarised as follows:

1. build a data-frame object by specifying your data-set
2. apply a series of transformations to your data
1. filter (e.g. apply some cuts) or
2. create a temporary column (e.g. the result of an expensive computation on branches, or an alias for a branch)
3. apply actions to the transformed data to produce results (e.g. fill a histogram) 4.

Keep reading to follow a five-minute crash course to TDataFrame, or jump to an overview of useful features, or a more in-depth explanation of transformations, actions and parallelism.

## Crash course

### Filling a histogram

// Fill a TH1F with the "MET" branch
ROOT::Experimental::TDataFrame d("myTree", filePtr); // build a TDataFrame like you would build a TTreeReader
auto h = d.Histo1D("MET");
h->Draw();

The first line creates a TDataFrame associated to the TTree "myTree". This tree has a branch named "MET".

Histo1D is an action; it returns a smart pointer (a TResultProxy to be precise) to a TH1F histogram filled with the MET of all events. If the quantity stored in the branch is a collection, the histogram is filled with its elements.

There are many other possible actions, and all their results are wrapped in smart pointers; we'll see why in a minute.

### Applying a filter

Let's now pretend we want to cut over the value of branch "MET" and count how many events pass this cut:

// Select events with "MET" greater than 4., count events that passed the selection
auto metCut = [](double x) { return x > 4.; }; // a c++11 lambda function checking "x > 4"
ROOT::Experimental::TDataFrame d("myTree", filePtr);
auto c = d.Filter(metCut, {"MET"}).Count();
std::cout << *c << std::endl;

Filter takes a function (a lambda in this example, but it can be any kind of function or even a functor class) and a list of branch names. The filter function is applied to the specified branches for each event; it is required to return a bool which signals whether the event passes the filter (true) or not (false). You can think of your data as "flowing" through the chain of calls, being transformed, filtered and finally used to perform actions. Multiple Filter calls can be chained one after another. It is possible to specify filters as strings too. This snippet is analogous to the one above:

ROOT::Experimental::TDataFrame d("myTree", filePtr);
auto c = d.Filter("MET > 4.").Count();
std::cout << *c << std::endl;

Here the names of the branches used in the expression and their types are inferred automatically. The string must be standard C++ and is just-in-time compiled by the ROOT interpreter, Cling.

### Running on a range of entries

It is sometimes necessary to limit the processing of the dataset to a range of entries. For this reason, the TDataFrame offers the concept of ranges as a node of the TDataFrame graph: this means that filters, columns and actions can be hung to it. If a range is specified after a filter, the range will act exclusively on the entries surviving the filter. Here you can find some code using ranges:

ROOT::Experimental::TDataFrame d("myTree", filePtr);
// This is how you can express a range of the first 30 entries
auto d_0_30 = d.Range(0, 30);
// This is how you pick all entries from 15 onwards
auto d_15_end = d.Range(15, 0);
// We can use a stride too, in this case we pick an event every 3
auto d_15_end_3 = d.Range(15, 0, 3);

Ranges are not available when multi-threading is enabled.

### Creating a temporary column

Let's now consider the case in which "myTree" contains two quantities "x" and "y", but our analysis relies on a derived quantity z = sqrt(x*x + y*y). Using the Define transformation, we can create a new column in the data-set containing the variable "z":

auto sqrtSum = [](double x, double y) { return sqrt(x*x + y*y); };
auto zCut = [](double z) { return z > 0.; }
ROOT::Experimental::TDataFrame d(treeName, filePtr);
auto zMean = d.Define("z", sqrtSum, {"x","y"})
.Filter(zCut, {"z"})
.Mean("z");
std::cout << *zMean << std::endl;

Define creates the variable "z" by applying sqrtSum to "x" and "y". Later in the chain of calls we refer to variables created with Define as if they were actual tree branches, but they are evaluated on the fly, once per event. As with filters, Define calls can be chained with other transformations to create multiple temporary columns. As with filters, it is possible to specify new columns as strings too. This snippet is analogous to the one above:

ROOT::Experimental::TDataFrame d(treeName, filePtr);
auto zMean = d.Define("z", "sqrt(x*x + y*y)")
.Filter("z > 0.")
.Mean("z");
std::cout << *zMean << std::endl;

Again the names of the branches used in the expression and their types are inferred automatically. The string must be standard C++ and is just-in-time compiled by the ROOT interpreter, Cling.

### Executing multiple actions

As a final example let us apply two different cuts on branch "MET" and fill two different histograms with the "pt\_v" of the filtered events. You should be able to easily understand what's happening:

// fill two histograms with the results of two opposite cuts
auto isBig = [](double x) { return x > 10.; };
ROOT::Experimental::TDataFrame d(treeName, filePtr);
auto h1 = d.Filter(isBig, {"MET"}).Histo1D("pt_v");
auto h2 = d.Histo1D("pt_v");
h1->Draw(); // event loop is run once here
h2->Draw("SAME"); // no need to run the event loop again

TDataFrame executes all above actions by running the event-loop only once. The trick is that actions are not executed at the moment they are called, but they are lazy, i.e. delayed until the moment one of their results is accessed through the smart pointer. At that time, the even loop is triggered and all results are produced simultaneously.

It is therefore good practice to declare all your filters and actions before accessing their results, allowing TDataFrame to loop once and produce all results in one go.

### Going parallel

Let's say we would like to run the previous examples in parallel on several cores, dividing events fairly between cores. The only modification required to the snippets would be the addition of this line before constructing the main data-frame object:

Simple as that, enjoy your speed-up.

## More features

Here is a list of the most important features that have been omitted in the "Crash course" for brevity's sake. You don't need to read all these to start using TDataFrame, but they are useful to save typing time and runtime.

### Default branch lists

When constructing a TDataFrame object, it is possible to specify a default branch list for your analysis, in the usual form of a list of strings representing branch names. The default branch list will be used as fallback whenever one specific to the transformation/action is not present.

// use "b1" and "b2" as default branches for Filter, Define and actions
ROOT::Experimental::TDataFrame d1(treeName, &file, {"b1","b2"});
// filter acts on default branch list, no need to specify it
auto h = d1.Filter([](int b1, int b2) { return b1 > b2; }).Histo1D("otherVar");
// just one default branch this time
ROOT::Experimental::TDataFrame d2(treeName, &file, {"b1"});
// we can still specify non-default branch lists
// Min here can fall back to the default "b1"
auto min = d2.Filter([](double b2) { return b2 > 0; }, {"b2"}).Min();

### Branch type guessing and explicit declaration of branch types

C++ is a statically typed language: all types must be known at compile-time. This includes the types of the TTree branches we want to work on. For filters, temporary columns and some of the actions, branch types are deduced from the signature of the relevant filter function/temporary column expression/action function:

// here b1 is deduced to be int and b2 to be double
dataFrame.Filter([](int x, double y) { return x > 0 && y < 0.; }, {"b1", "b2"});

If we specify an incorrect type for one of the branches, an exception with an informative message will be thrown at runtime, when the branch value is actually read from the TTree: the implementation of TDataFrame allows the detection of type mismatches. The same would happen if we swapped the order of "b1" and "b2" in the branch list passed to Filter.

Certain actions, on the other hand, do not take a function as argument (e.g. Histo1D), so we cannot deduce the type of the branch at compile-time. In this case **TDataFrame tries to guess the type of the branch**, trying out the most common ones and std::vector thereof. This is why we never needed to specify the branch types for all actions in the above snippets.

When the branch type is not a common one such as int, double, char or float it is therefore good practice to specify it as a template parameter to the action itself, like this:

dataFrame.Histo1D("b1"); // OK if b1 is a "common" type
dataFrame.Histo1D<Object_t>("myObject"); // OK, "myObject" is deduced to be of type Object_t
// dataFrame.Histo1D("myObject"); // THROWS an exception

### Generic actions

TDataFrame strives to offer a comprehensive set of standard actions that can be performed on each event. At the same time, it allows users to execute arbitrary code (i.e. a generic action) inside the event loop through the Foreach and ForeachSlot actions.

Foreach(f, branchList) takes a function f (lambda expression, free function, functor...) and a list of branches, and executes f on those branches for each event. The function passed must return nothing (i.e. void). It can be used to perform actions that are not already available in the interface. For example, the following snippet evaluates the root mean square of branch "b":

// Single-thread evaluation of RMS of branch "b" using Foreach
double sumSq = 0.;
unsigned int n = 0;
ROOT::Experimental::TDataFrame d("bTree", bFilePtr);
d.Foreach([&sumSq, &n](double b) { ++n; sumSq += b*b; }, {"b"});
std::cout << "rms of b: " << std::sqrt(sumSq / n) << std::endl;

When executing on multiple threads, users are responsible for the thread-safety of the expression passed to Foreach. The code above would need to employ some resource protection mechanism to ensure non-concurrent writing of rms; but this is probably too much head-scratch for such a simple operation.

ForeachSlot can help in this situation. It is an alternative version of Foreach for which the function takes an additional parameter besides the branches it should be applied to: an unsigned int slot parameter, where slot is a number indicating which thread (0, 1, 2 , ..., poolSize - 1) the function is being run in. We can take advantage of ForeachSlot to evaluate a thread-safe root mean square of branch "b":

// Thread-safe evaluation of RMS of branch "b" using ForeachSlot
unsigned int nSlots = ROOT::GetImplicitMTPoolSize();
std::vector<double> sumSqs(nSlots, 0.);
std::vector<unsigned int> ns(nSlots, 0);
ROOT::Experimental::TDataFrame d("bTree", bFilePtr);
d.ForeachSlot([&sumSqs, &ns](unsigned int slot, double b) { sumSqs[slot] += b*b; ns[slot] += 1; }, {"b"});
double sumSq = std::accumulate(sumSqs.begin(), sumSqs.end(), 0.); // sum all squares
unsigned int n = std::accumulate(ns.begin(), ns.end(), 0); // sum all counts
std::cout << "rms of b: " << std::sqrt(sumSq / n) << std::endl;

You see how we created one double variable for each thread in the pool, and later merged their results via std::accumulate.

### Call graphs (storing and reusing sets of transformations)

Sets of transformations can be stored as variables** and reused multiple times to create call graphs in which several paths of filtering/creation of branches are executed simultaneously; we often refer to this as "storing the state of the chain".

This feature can be used, for example, to create a temporary column once and use it in several subsequent filters or actions, or to apply a strict filter to the data-set before executing several other transformations and actions, effectively reducing the amount of events processed.

Let's try to make this clearer with a commented example:

// build the data-frame and specify a default branch list
ROOT::Experimental::TDataFrame d(treeName, filePtr, {"var1", "var2", "var3"});
// apply a cut and save the state of the chain
auto filtered = d.Filter(myBigCut);
// plot branch "var1" at this point of the chain
auto h1 = filtered.Histo1D("var1");
// create a new branch "vec" with a vector extracted from a complex object (only for filtered entries)
// and save the state of the chain
auto newBranchFiltered = filtered.Define("vec", [](const Obj& o) { return o.getVector(); }, {"obj"});
// apply a cut and fill a histogram with "vec"
auto h2 = newBranchFiltered.Filter(cut1).Histo1D("vec");
// apply a different cut and fill a new histogram
auto h3 = newBranchFiltered.Filter(cut2).Histo1D("vec");
// Inspect results
h3->Draw("SAME"); // event loop does not need to be run again here..
std::cout << "Entries in h1: " << h1->GetEntries() << std::endl; // ..or here

TDataFrame detects when several actions use the same filter or the same temporary column, and only evaluates each filter or temporary column once per event, regardless of how many times that result is used down the call graph. Objects read from each branch are built once and never copied, for maximum efficiency. When "upstream" filters are not passed, subsequent filters, temporary column expressions and actions are not evaluated, so it might be advisable to put the strictest filters first in the chain.

## Transformations

### Filters

A filter is defined through a call to Filter(f, branchList). f can be a function, a lambda expression, a functor class, or any other callable object. It must return a bool signalling whether the event has passed the selection (true) or not (false). It must perform "read-only" actions on the branches, and should not have side-effects (e.g. modification of an external or static variable) to ensure correct results when implicit multi-threading is active.

TDataFrame only evaluates filters when necessary: if multiple filters are chained one after another, they are executed in order and the first one returning false causes the event to be discarded and triggers the processing of the next entry. If multiple actions or transformations depend on the same filter, that filter is not executed multiple times for each entry: after the first access it simply serves a cached result.

#### Named filters and cutflow reports

An optional string parameter name can be passed to the Filter method to create a named filter. Named filters work as usual, but also keep track of how many entries they accept and reject.

Statistics are retrieved through a call to the Report method:

• when Report is called on the main TDataFrame object, it prints stats for all named filters declared up to that point
• when called on a stored chain state (i.e. a chain/graph node), it prints stats for all named filters in the section of the chain between the main TDataFrame and that node (included).

Stats are printed in the same order as named filters have been added to the graph, and refer to the latest event-loop that has been run using the relevant TDataFrame. If Report is called before the event-loop has been run at least once, a run is triggered.

### Ranges

When TDataFrame is not being used in a multi-thread environment (i.e. no call to EnableImplicitMT was made), Range transformations are available. These act very much like filters but instead of basing their decision on a filter expression, they rely on start,stop and stride parameters.

• start: number of entries that will be skipped before starting processing again
• stop: maximum number of entries that will be processed
• stride: only process one entry every stride entries

The actual number of entries processed downstream of a Range node will be (stop - start)/stride (or less if less entries than that are available).

Note that ranges act "locally", not based on the global entry count: Range(10,50) means "skip the first 10 entries that reach this node*, let the next 40 entries pass, then stop processing". If a range node hangs from a filter node, and the range has a start parameter of 10, that means the range will skip the first 10 entries that pass the preceding filter.

Ranges allow "early quitting": if all branches of execution of a functional graph reached their stop value of processed entries, the event-loop is immediately interrupted. This is useful for debugging and initial explorations.

### Temporary columns

Temporary columns are created by invoking Define(name, f, branchList). As usual, f can be any callable object (function, lambda expression, functor class...); it takes the values of the branches listed in branchList (a list of strings) as parameters, in the same order as they are listed in branchList. f must return the value that will be assigned to the temporary column.

A new variable is created called name, accessible as if it was contained in the dataset from subsequent transformations/actions.

Use cases include:

• caching the results of complex calculations for easy and efficient multiple access
• extraction of quantities of interest from complex objects
• branch aliasing, i.e. changing the name of a branch

An exception is thrown if the name of the new branch is already in use for another branch in the TTree.

It is also possible to specify the quantity to be stored in the new temporary column as a C++ expression with the method Define(name, expression). For example this invocation

tdf.Define("pt", "sqrt(px*px + py*py)");

will create a new column called "pt" the value of which is calculated starting from the branches px and py. The system builds a just-in-time compiled function starting from the expression after having deduced the list of necessary branches from the names of the variables specified by the user.

## Actions

### Instant and lazy actions

Actions can be instant or lazy. Instant actions are executed as soon as they are called, while lazy actions are executed whenever the object they return is accessed for the first time. As a rule of thumb, actions with a return value are lazy, the others are instant.

### Overview

Here is a quick overview of what actions are present and what they do. Each one is described in more detail in the reference guide.

In the following, whenever we say an action "returns" something, we always mean it returns a smart pointer to it. Also note that all actions are only executed for events that pass all preceding filters.

Lazy actions Description
Count Return the number of events processed.
Fill Fill a user-defined object with the values of the specified branches, as if by calling Obj.Fill(branch1, branch2, ...).
Histo{1D,2D,3D} Fill a {one,two,three}-dimensional histogram with the processed branch values.
Max Return the maximum of processed branch values.
Mean Return the mean of processed branch values.
Min Return the minimum of processed branch values.
Profile{1D,2D} Fill a {one,two}-dimensional profile with the branch values that passed all filters.
Reduce Reduce (e.g. sum, merge) entries using the function (lambda, functor...) passed as argument. The function must have signature T(T,T) where T is the type of the branch. Return the final result of the reduction operation. An optional parameter allows initialization of the result object to non-default values.
Take Build a collection of values of a branch.
Instant actions Description
Foreach Execute a user-defined function on each entry. Users are responsible for the thread-safety of this lambda when executing with implicit multi-threading enabled.
ForeachSlot Same as Foreach, but the user-defined function must take an extra unsigned int slot as its first parameter. slot will take a different value, 0 to nThreads - 1, for each thread of execution. This is meant as a helper in writing thread-safe Foreach actions when using TDataFrame after ROOT::EnableImplicitMT(). ForeachSlot works just as well with single-thread execution: in that case slot will always be 0.
Snapshot Writes on disk a dataset made of the selected columns and entries passing the filters (if any).
Queries Description
Report This is not properly an action, since when Report is called it does not book an operation to be performed on each entry. Instead, it interrogates the data-frame directly to print a cutflow report, i.e. statistics on how many entries have been accepted and rejected by the filters. See the section on named filters for a more detailed explanation.

## Parallel execution

As pointed out before in this document, TDataFrame can transparently perform multi-threaded event loops to speed up the execution of its actions. Users only have to call ROOT::EnableImplicitMT() before constructing the TDataFrame object to indicate that it should take advantage of a pool of worker threads. Each worker thread processes a distinct subset of entries, and their partial results are merged before returning the final values to the user.

Filter and Define transformations should be inherently thread-safe: they have no side-effects and are not dependent on global state. Most Filter/Define functions will in fact be pure in the functional programming sense. All actions are built to be thread-safe with the exception of Foreach, in which case users are responsible of thread-safety, see here.

Definition at line 36 of file TDataFrame.hxx.

## Public Member Functions

TDataFrame (std::string_view treeName, std::string_view filenameglob, const ColumnNames_t &defaultBranches={})
Build the dataframe. More...

template<typename FILENAMESCOLL = std::vector<std::string>, typename std::enable_if< TDFInternal::TIsContainer< FILENAMESCOLL >::fgValue &&!std::is_same< std::string, FILENAMESCOLL >::value, int >::type = 0>
TDataFrame (std::string_view treeName, const FILENAMESCOLL &filenamescoll, const ColumnNames_t &defaultBranches={})
Build the dataframe. More...

TDataFrame (std::string_view treeName, ::TDirectory *dirPtr, const ColumnNames_t &defaultBranches={})

TDataFrame (TTree &tree, const ColumnNames_t &defaultBranches={})
Build the dataframe. More...

TDataFrame (Long64_t numEntries)
Build the dataframe. More...

Public Member Functions inherited from ROOT::Experimental::TDF::TInterface< TDFDetail::TLoopManager >
TResultProxy< unsigned int > Count ()
Return the number of entries processed (lazy action) More...

TInterface< TCustomColumnBaseDefine (std::string_view name, F expression, const ColumnNames_t &bl={})
Creates a temporary branch. More...

TInterface< TCustomColumnBaseDefine (std::string_view name, std::string_view expression)
Creates a temporary branch. More...

TResultProxy< T > Fill (T &&model, const ColumnNames_t &bl)
Fill and return any entity with a Fill method (lazy action) More...

TResultProxy< T > Fill (T &&model, const ColumnNames_t &bl)

TInterface< TFilterBaseFilter (F f, const ColumnNames_t &bn={}, std::string_view name="")
Append a filter to the call graph. More...

TInterface< TFilterBaseFilter (F f, std::string_view name)
Append a filter to the call graph. More...

TInterface< TFilterBaseFilter (F f, const std::initializer_list< std::string > &bn)
Append a filter to the call graph. More...

TInterface< TFilterBaseFilter (std::string_view expression, std::string_view name="")
Append a filter to the call graph. More...

void Foreach (F f, const ColumnNames_t &bl={})
Execute a user-defined function on each entry (instant action) More...

void ForeachSlot (F f, const ColumnNames_t &bl={})
Execute a user-defined function requiring a processing slot index on each entry (instant action) More...

TResultProxy<::TH1FHisto1D (::TH1F &&model=::TH1F{"", "", 128u, 0., 0.}, std::string_view vName="")
Fill and return a one-dimensional histogram with the values of a branch (lazy action) More...

TResultProxy<::TH1FHisto1D (std::string_view vName)

TResultProxy<::TH1FHisto1D (::TH1F &&model, std::string_view vName, std::string_view wName)
Fill and return a one-dimensional histogram with the values of a branch (lazy action) More...

TResultProxy<::TH1FHisto1D (std::string_view vName, std::string_view wName)

TResultProxy<::TH1FHisto1D (::TH1F &&model=::TH1F{"", "", 128u, 0., 0.})

TResultProxy<::TH2FHisto2D (::TH2F &&model, std::string_view v1Name="", std::string_view v2Name="")
Fill and return a two-dimensional histogram (lazy action) More...

TResultProxy<::TH2FHisto2D (::TH2F &&model, std::string_view v1Name, std::string_view v2Name, std::string_view wName)
Fill and return a two-dimensional histogram (lazy action) More...

TResultProxy<::TH2FHisto2D (::TH2F &&model)

TResultProxy<::TH3FHisto3D (::TH3F &&model, std::string_view v1Name="", std::string_view v2Name="", std::string_view v3Name="")
Fill and return a three-dimensional histogram (lazy action) More...

TResultProxy<::TH3FHisto3D (::TH3F &&model, std::string_view v1Name, std::string_view v2Name, std::string_view v3Name, std::string_view wName)
Fill and return a three-dimensional histogram (lazy action) More...

TResultProxy<::TH3FHisto3D (::TH3F &&model)

TResultProxy< double > Max (std::string_view branchName="")
Return the maximum of processed branch values (lazy action) More...

TResultProxy< double > Mean (std::string_view branchName="")
Return the mean of processed branch values (lazy action) More...

TResultProxy< double > Min (std::string_view branchName="")
Return the minimum of processed branch values (lazy action) More...

TResultProxy<::TProfileProfile1D (::TProfile &&model, std::string_view v1Name="", std::string_view v2Name="")
Fill and return a one-dimensional profile (lazy action) More...

TResultProxy<::TProfileProfile1D (::TProfile &&model, std::string_view v1Name, std::string_view v2Name, std::string_view wName)
Fill and return a one-dimensional profile (lazy action) More...

TResultProxy<::TProfileProfile1D (::TProfile &&model)

TResultProxy<::TProfile2DProfile2D (::TProfile2D &&model, std::string_view v1Name="", std::string_view v2Name="", std::string_view v3Name="")
Fill and return a two-dimensional profile (lazy action) More...

TResultProxy<::TProfile2DProfile2D (::TProfile2D &&model, std::string_view v1Name, std::string_view v2Name, std::string_view v3Name, std::string_view wName)
Fill and return a two-dimensional profile (lazy action) More...

TResultProxy<::TProfile2DProfile2D (::TProfile2D &&model)

TInterface< TRangeBaseRange (unsigned int start, unsigned int stop, unsigned int stride=1)
Creates a node that filters entries based on range. More...

TInterface< TRangeBaseRange (unsigned int stop)
Creates a node that filters entries based on range. More...

TResultProxy< T > Reduce (F f, std::string_view branchName={})
Execute a user-defined reduce operation on the values of a branch. More...

TResultProxy< T > Reduce (F f, std::string_view branchName, const T &initValue)
Execute a user-defined reduce operation on the values of a branch. More...

void Report ()
Print filtering statistics on screen. More...

TInterface< TLoopManagerSnapshot (std::string_view treename, std::string_view filename, const ColumnNames_t &bnames)
Create a snapshot of the dataset on disk in the form of a TTree. More...

TInterface< TLoopManagerSnapshot (std::string_view treename, std::string_view filename, const ColumnNames_t &bnames)
Create a snapshot of the dataset on disk in the form of a TTree. More...

TInterface< TLoopManagerSnapshot (std::string_view treename, std::string_view filename, std::string_view columnNameRegexp="")
Create a snapshot of the dataset on disk in the form of a TTree. More...

TResultProxy< COLL > Take (std::string_view branchName="")
Return a collection of values of a branch (lazy action) More...

## Private Types

using ColumnNames_t = TDFDetail::ColumnNames_t

Protected Member Functions inherited from ROOT::Experimental::TDF::TInterface< TDFDetail::TLoopManager >
TInterface (const std::shared_ptr< TDFDetail::TLoopManager > &proxied, const std::weak_ptr< TLoopManager > &impl)

TInterface (const std::shared_ptr< TDFDetail::TLoopManager > &proxied)
Only enabled when building a TInterface<TLoopManager> More...

std::shared_ptr< TLoopManagerGetDataFrameChecked ()
Get the TLoopManager if reachable. If not, throw. More...

const ColumnNames_t GetDefaultBranchNames (unsigned int nExpectedBranches, std::string_view actionNameForErr)

TInterface< TLoopManagerSnapshotImpl (std::string_view treename, std::string_view filename, const ColumnNames_t &bnames, TDFInternal::TStaticSeq< S... >)
Implementation of snapshot. More...

Protected Attributes inherited from ROOT::Experimental::TDF::TInterface< TDFDetail::TLoopManager >
std::weak_ptr< TLoopManagerfImplWeakPtr

std::shared_ptr< TDFDetail::TLoopManagerfProxiedPtr

#include <ROOT/TDataFrame.hxx>

Inheritance diagram for ROOT::Experimental::TDataFrame:
[legend]

## ◆ ColumnNames_t

 using ROOT::Experimental::TDataFrame::ColumnNames_t = TDFDetail::ColumnNames_t
private

Definition at line 37 of file TDataFrame.hxx.

## ◆ TDataFrame() [1/5]

 TDataFrame::TDataFrame ( std::string_view treeName, std::string_view filenameglob, const ColumnNames_t & defaultBranches = {} )

Build the dataframe.

Parameters
 [in] treeName Name of the tree contained in the directory [in] filenameglob TDirectory where the tree is stored, e.g. a TFile. [in] defaultBranches Collection of default branches.

The default branches are looked at in case no branch is specified in the booking of actions or transformations. See TInterface for the documentation of the methods available.

Definition at line 531 of file TDataFrame.cxx.

## ◆ TDataFrame() [2/5]

template<typename FILENAMESCOLL , typename std::enable_if< TDFInternal::TIsContainer< FILENAMESCOLL >::fgValue &&!std::is_same< std::string, FILENAMESCOLL >::value, int >::type >
 ROOT::Experimental::TDataFrame::TDataFrame ( std::string_view treeName, const FILENAMESCOLL & filenamescoll, const ColumnNames_t & defaultBranches = {} )

Build the dataframe.

Template Parameters
 FILENAMESCOLL The type of the file collection: only requirement: must have begin and end.
Parameters
 [in] treeName Name of the tree contained in the directory [in] filenamescoll Collection of file names, for example a list of strings. [in] defaultBranches Collection of default branches.

The default branches are looked at in case no branch is specified in the booking of actions or transformations. See TInterface for the documentation of the methods available.

Definition at line 65 of file TDataFrame.hxx.

## ◆ TDataFrame() [3/5]

 ROOT::Experimental::TDataFrame::TDataFrame ( std::string_view treeName, ::TDirectory * dirPtr, const ColumnNames_t & defaultBranches = {} )

## ◆ TDataFrame() [4/5]

 TDataFrame::TDataFrame ( TTree & tree, const ColumnNames_t & defaultBranches = {}` )

Build the dataframe.

Parameters
 [in] tree The tree or chain to be studied. [in] defaultBranches Collection of default branches.

The default branches are looked at in case no branch is specified in the booking of actions or transformations. See TInterface for the documentation of the methods available.

Definition at line 551 of file TDataFrame.cxx.

## ◆ TDataFrame() [5/5]

 TDataFrame::TDataFrame ( Long64_t numEntries )

Build the dataframe.

Parameters
 [in] numEntries The number of entries to generate.

An empty-source dataframe constructed with a number of entries will generate those entries on the fly when some action is triggered, and it will do so for all the previously-defined temporary branches.

Definition at line 563 of file TDataFrame.cxx.

The documentation for this class was generated from the following files: