doc/v620/pyroot002__TTreeAsMatrix_8py.html

import ROOT

from sys import exit


try:

    import numpy as np

except:

    print("Failed to import numpy.")

    exit()


# Helper function to create an example tree

def make_example():

    root_file = ROOT.TFile("pyroot002_example.root", "RECREATE")

    tree = ROOT.TTree("tree", "tutorial")

    x = np.empty((1), dtype="float32")

    y = np.empty((1), dtype="float32")

    tree.Branch("x", x, "x/F")

    tree.Branch("y", y, "y/F")


    for i in range(4):

        x[0] = i

        y[0] = -i

        tree.Fill()

    root_file.Write()


    return (root_file, x, y), tree


# The conversion of the TTree to a numpy array is implemented with multi-

# thread support.

ROOT.ROOT.EnableImplicitMT()


# Create a ROOT file with a tree and the branches "x" and "y"

_, tree = make_example()


# Print content of the tree by looping explicitly

print("Tree content:\n{}\n".format(

    np.asarray([[tree.x, tree.y] for event in tree])))


# Read-out full tree as numpy array

array = tree.AsMatrix()

print("Tree converted to a numpy array:\n{}\n".format(array))


# Get numpy array and according labels of the columns

array, labels = tree.AsMatrix(return_labels=True)

print("Return numpy array and labels:\n{}\n{}\n".format(labels, array))


# Apply numpy methods on the data

print("Mean of the columns retrieved with a numpy method: {}\n".format(

    np.mean(array, axis=0)))


# Read only specific branches

array = tree.AsMatrix(columns=["x"])

print("Only the content of the branch 'x':\n{}\n".format(np.squeeze(array)))


array = tree.AsMatrix(exclude=["x"])

print("Read all branches except 'x':\n{}\n".format(np.squeeze(array)))


# Get an array with a specific data-type

array = tree.AsMatrix(dtype="int")

print("Return numpy array with data-type 'int':\n{}\n".format(array))


## Convert the tree to a pandas.DataFrame

try:

    import pandas

except:

    print("Failed to import pandas.")

    exit()


data, columns = tree.AsMatrix(return_labels=True)

df = pandas.DataFrame(data=data, columns=columns)

print("Tree converted to a pandas.DataFrame:\n{}".format(df))