Graphs tutorials

Examples showing the "graphs classes" usage.

A TGraph is an object made of two arrays X and Y with n points each. ROOT can create TGraphs automatically by reading a text file (e.g. CSV), using a function, another TGraph, histogram, vectors, arrays, or even by adding pairs of points one by one.

In addition, ROOT offers multiple variations to basic TGraphs, such as:

• TGraph2D
• TGraph2DAsymmErrors
• TGraph2DErrrors
• TGraphAsymmErrors
• TGraphBentErrors
• TGraphDelaunay
• TGraphDelaunay2D
• TGraphErrors
• TGraphMultiErrors
• TGraphPolar
• TGraphQQ
• TGraphSmooth
• TGraphStruct
• TGraphTime.

TGraphs are painted through the TGraphPainter or TGraph2DPainter classes. As a general remark, TGraphs are not binned, each point is painted individually.

The graph tutorials below are divided in groups of increasing complexity, starting with examples showing how to create, fill, and draw the different types of graphs.

Tutorials sorted after groups

• Basics: creation and drawing
• Formatting: changing/adding elements to the graphs and/or the plots
• Intermediate: more advanced examples
• More tutorials

List of all tutorials

Basics

These examples showcase the creation of different types of graphs and basic ways to plot them.

Tutorial		Description
gr001_simple.C		Create a simple graph from available data or from a file, and draw it.
gr002_errors.C		Create and draw a graph with error bars.
gr003_errors2.C		Create and draw two graphs with error bars, superposed on the same canvas (not using TMultiGraph).
gr004_errors_asym.C		Create and draw a graph with asymmetric x & y errors.
gr005_apply.C		Demonstrate the functionality of the TGraph::Apply() method.
gr006_scatter.C		Scatter plot for 4 variables, mapped to: x, y, marker color and marker size.
gr007_multigraph.C		Create and draw a TMultiGraph (several graphs superposed).
gr008_multierrors.C		Graph with multiple y errors in each bin.
gr009_bent_err.C	gr009_bent_err.py	Graph with bent (non-vertical/non-horizontal) error bars.
gr010_approx_smooth.C		Create a TGraphSmooth and show the usage of the interpolation function Approx.
gr011_graph2d_errorsfit.C		Create, draw and fit a TGraph2DErrors.
gr012_polar.C		Create and draw a polar graph.
gr013_polar2.C		Polar graph with errors and polar axis in radians (PI fractions).
gr014_polar3.C		Create a polar graph using a TF1 and draw it with PI axis.
gr015_smooth.C		Show scatter plot smoothers: ksmooth, lowess, supsmu
gr016_struct.C		Draw a simple graph structure.
gr017_time.C		Example of TGraphTime.
gr018_time2.C		TGraphTime to visualize a set of particles with their time stamp in a MonteCarlo program.

Formatting

These examples show different ways of formatting the graphs, in particular how to:

Tutorial		Description
gr101_shade_area.C		Shade an area between two graphs.
gr102_reverse_graph.C		Reverse points of a graph along x.
gr103_zones.C	gr103_zones.py	Divide a canvas into adjacent subpads, with axis labels on the top and right side of the pads.
gr104_palettecolor.C		Automatically set graph colors from a palette.
gr105_multigraphpalettecolor.C		Automatically set multi-graph colors from a palette.
gr106_exclusiongraph.C		Draw three graphs (in a TMultiGraph) with exclusion zones.
gr107_exclusiongraph2.C		Draw graphs (superposed, but no TMultiGraph) with exclusion zones.
gr108_timeSeriesFromCSV.C	gr108_timeSeriesFromCSV.py	Use of the time axis on a TGraph with data read from a text file.
gr109_timeSeriesFromCSV_RDF.C		Use of the time axis on a TGraph with data read from a text file, but using RDataFrame.
gr110_logscale.C		Set logarithmic scale for the axes of the graph.
gr111_legend.C		Add a legend.
gr112_reverse_graph_and_errors.C		Reverse points of the graph along both axes - examples with various error types.

Intermediate

These examples are slightly more advanced so will be most useful for more advanced users.

Tutorial	Description
gr201_waves.C	Draw spherical waves interference, using closed and filled TGraphs to hide other plot elements.
gr202_textmarkers.C	Draw a graph with text attached to each point. Uses a TExec function to attach the text to the points.

More tutorials

These examples show the most complex usage of the graphs functionality.

Tutorial	Description
gr301_highlight1.C	How to use the interactive highlight mode on graph, thanks to the TCanvas HighlightConnect method.
gr302_highlight2.C	How to use the interactive highlight mode on graph, thanks to the TCanvas HighlightConnect method.
gr303_zdemo.C	Example of graphs in log scales with annotations and other advanced plot formatting.

Files
file	gr001_simple.C
	This tutorial demonstrates how to create simple graphs in ROOT.
file	gr002_errors.C
	Create and draw a graph with error bars.
file	gr003_errors2.C
	Create and draw two graphs with error bars, superposed on the same canvas
file	gr004_errors_asym.C
	This tutorial demonstrates the use of TGraphAsymmErrors to plot a graph with asymmetrical errors on both the x and y axes.
file	gr005_apply.C
	A macro to demonstrate the functionality of TGraph::Apply() method.
file	gr006_scatter.C
	Draw a scatter plot for 4 variables, mapped to: x, y, marker colour and marker size.
file	gr007_multigraph.C
	TMultiGraph is used to combine multiple graphs into one plot.
file	gr008_multierrors.C
	Draw a graph with multiple errors.
file	gr009_bent_err.C
	Graph with bent error bars.
file	gr009_bent_err.py
	Graph with bent error bars.
file	gr010_approx_smooth.C
	Create a TGraphSmooth and show the usage of the interpolation function Approx.
file	gr011_graph2d_errorsfit.C
	Create, draw and fit a TGraph2DErrors.
file	gr012_polar.C
	Create and draw a polar graph.
file	gr013_polar2.C
	Create and draw a polar graph with errors and polar axis in radians (PI fractions).
file	gr014_polar3.C
	Create a polar graph using a TF1 and draw it with PI axis.
file	gr015_smooth.C
	Show scatter plot smoothers: ksmooth, lowess, supsmu, as described in: Modern Applied Statistics with S-Plus, 3rd Edition W.N.
file	gr016_struct.C
	Draw a simple graph structure.
file	gr017_time.C
	Example of TGraphTime.
file	gr018_time2.C
	Example of TGraphTime showing how the class could be used to visualize a set of particles with their time stamp in a MonteCarlo program.
file	gr101_shade_area.C
	Show how to shade an area between two graphs.
file	gr102_reverse_graph.C
	This example tests the reverse graphs obtained with Draw("a pl rx ry ") on a TGraph, where rx and ry refere to the reversing of x and y axis.
file	gr103_zones.C
	Example of script showing how to divide a canvas into adjacent subpads + axis labels on the top and right side of the pads.
file	gr103_zones.py
	Example of script showing how to divide a canvas into adjacent subpads + axis labels on the top and right side of the pads.
file	gr104_palettecolor.C
	Palette coloring for graphs is activated thanks to the options PFC (Palette Fill Color), PLC (Palette Line Color) and AMC (Palette Marker Color).
file	gr105_multigraphpalettecolor.C
	Palette coloring for multi-graphs is activated thanks to the options PFC (Palette Fill Color), PLC (Palette Line Color) and AMC (Palette Marker Color).
file	gr106_exclusiongraph.C
	Draw three graphs with an exclusion zone.
file	gr107_exclusiongraph2.C
	Draw several graphs with exclusion zones.
file	gr108_timeSeriesFromCSV.C
	This macro illustrates the use of the time axis on a TGraph with data read from a text file containing the SWAN usage statistics during July 2017.
file	gr108_timeSeriesFromCSV.py
	This macro illustrates the use of the time axis on a TGraph with data read from a text file containing the SWAN usage statistics during July 2017.
file	gr109_timeSeriesFromCSV_RDF.C
	This macro illustrates the use of the time axis on a TGraph with data read from a text file containing the SWAN usage statistics during July 2017.
file	gr110_logscale.C
	This tutorial demonstrates how to set a logarithmic scale for the axes of a graph using the SetLogScale() method.
file	gr111_legend.C
	Simple graph with legend.
file	gr112_reverse_graph_and_errors.C
	This example tests all the various cases of reverse graphs obtained with Draw("a pl rx ry "), where rx and ry refer to the reversing of x and y axis.
file	gr201_waves.C
	Draw spherical waves interference.
file	gr202_textmarkers.C
	Draw a graph with text attached to each point.
file	gr301_highlight1.C
	This tutorial demonstrates how to use the highlight mode on graph, thanks to the TCanvas HighlightConnect method.
file	gr302_highlight2.C
	This tutorial demonstrates how to use the highlight mode on graph, thanks to the TCanvas HighlightConnect method.
file	gr303_zdemo.C
	This macro is an example of graphs in log scales with annotations.