Histograms tutorials

Examples showing the "histograms' classes" usage.

A histogram is a visual representation of the distribution of quantitative data. TH1 class introduces the basic data structure used in root for histograms.

In a nutshell:

// Open the file to write the histogram to
 auto outFile = std::unique_ptr<TFile>(TFile::Open("outfile.root", "RECREATE"));
 
 // Create the histogram object
 // There are several constructors you can use (\see TH1). In this example we use the
 // simplest one, accepting a number of bins and a range.
 int nBins = 30;
 double rangeMin = 0.0;
 double rangeMax = 10.0;
 TH1D histogram("histogram", "My first ROOT histogram", nBins, rangeMin, rangeMax);
 
 // Fill the histogram. In this simple example we use a fake set of data.
 // The 'D' in TH1D stands for 'double', so we fill the histogram with doubles.
 // In general you should prefer TH1D over TH1F unless you have a very specific reason
 // to do otherwise.
 const std::array values{1, 2, 3, 3, 3, 4, 3, 2, 1, 0};
 for (double val : values) {
    histogram.Fill(val);
 }
 
 // Write the histogram to `outFile`.
 outFile->WriteObject(&histogram, histogram.GetName());
 
 // When the TFile goes out of scope it will close itself and write its contents to disk.

Explore the examples below for different histogram classes

Tutorials sorted after groups

• Introduction
• TH1 Histograms
• TH2 Histograms
• [ThnSparse] (thnsparse)
• THStack
• TRatio plots
• TPoly
• Graphics
• TExec

List of all tutorials

Introduction

Tutorial	Description
hist000_TH1_first.C	First example.

TH1 Histograms

These examples shows some of the ratioplots

Tutorial		Description
hist000_TH1_first.C		Hello World example for TH1.
hist001_TH1_fillrandom.C	hist001_TH1_fillrandom.py	Fill a 1D histogram with random values using predefined functions.
hist002_TH1_fillrandom_userfunc.C		Fill a 1D histogram from a user-defined parametric function.
hist003_TH1_draw.C		Draw a 1D histogram to a canva.
hist004_TH1_labels.C		1D histograms with alphanumeric labels.
hist005_TH1_palettecolor.C		Palette coloring for TH1.
hist006_TH1_bar_charts.C		Draw 1D histograms as bar charts.
hist007_TH1_liveupdate.C	hist007_TH1_liveupdate.py	Histograms filled and drawn in a loop.
hist008_TH1_zoom.C		Change the range of an axis in a Histogram.
hist009_TH1_normalize.C		Normalizing a Histogram.
hist010_TH1_two_scales.C	hist010_TH1_two_scales.py	Draw two histograms on one canva using different y-axis scales.
hist011_TH1_legend_autoplaced.C		Automatic placing of the legend.
hist012_TH1_hksimple.C		Dynamic filling of TH1K histograms.
hist013_TH1_rebin.C		Create a variable bin-width histogram and change bin sizes.
hist014_TH1_cumulative.C		Illustrate use of the TH1::GetCumulative method.
hist015_TH1_read_and_draw.C	hist015_TH1_read_and_draw.py	Read a 1D histogram from a ROOT File and draw it.
hist016_TH1_different_scales_canvas.C		Draw two histograms on one canva using different y-axis scales.
hist017_TH1_smooth.C		Histogram smoothing.
hist060_TH1_Stats.C		Edit statistics box.
hist101_TH1_autobinning.C		Fill multiple histograms with different functions and automatic binning.

TH2 Histograms

Tutorial	Description
hist018_TH2_cutg.C	Use TCutG object to select bins for drawing a region of a 2D histogram.
hist019_TH2_projection.C	Display a histogram and its two projections.
hist020_TH2_draw.C	Display 2D histogram drawing options.
hist021_TH2_reverse_axis.C	Histogram with reverse axis.
hist022_TH2_palette.C	Automatic placing of a color palette via option COLZ.
hist102_TH2_contour_list.C	Get contours from a 2D histogram.

THnSparse

Tutorial	Description
hist103_THnSparse_hist.C	Evaluate the performance of THnSparse vs TH1/2/3/n.

THStack

Tutorial	Description
hist023_THStack_simple.C	Stack histograms with class THStack.
hist024_THStack_pads.C	Draw stack histograms on subpads.
hist025_THStack_2d_palette_color.C	Display multiple 2D histograms picking colors within palette 1.
hist026_THStack_color_scheme.C	Use accessible color schemes with THStack.
hist027_THStack_palette_color.C	Display multiple 1D histograms picking colors within palette kOcean.
hist028_THStack_multicolor.C	Use a THStack to show a 2D histogram with cells with different colors.

Ratio plots

Tutorial		Description
hist029_TRatioPlot_simple.C	hist029_TRatioPlot_simple.py	Create a simple ratio plot of two histograms using the pois division option.
hist030_TRatioPlot_residual.C	hist030_TRatioPlot_residual.py	Create a fit residual plot.
hist031_TRatioPlot_residual_fit.C	hist031_TRatioPlot_residual_fit.py	Create a fit residual plot and set the y-axis range for it.
hist032_TRatioPlot_fit_lines.C	hist032_TRatioPlot_fit_lines.py	Set custom dashed lines specified by a vector of floats.
hist033_TRatioPlot_fit_confidence.C	hist033_TRatioPlot_fit_confidence.py	Set the colors of the confidence interval bands by using
hist034_TRatioPlot_fit_margin.C	hist034_TRatioPlot_fit_margin.py	Create a fit residual plot, where the separation margin has been set to 0.

TPoly

Tutorial	Description
hist037_TH2Poly_boxes.C	Create a histogram with polygonal bins (TH2Poly).
hist038_TH2Poly_honeycomb.C	Create a histogram with hexagonal bins (TH2Poly).
hist039_TH2Poly_usa.C	Create a histogram with polygonal bins (TH2Poly). The initial data represent the USA map.
hist040_TH2Poly_europe.C	Create a histogram with polygonal bins (TH2Poly). The initial data represent the Europe map.
hist041_TProfile2Poly_realistic.C	Create a histogram with polygonal bins representing different particle charges in a detectior.
hist042_TProfile2Poly_module_error.C	Create a histogram with polygonal bins simulating a faulty detector panel w.r.t. particle charge.
hist056_TPolyMarker_contour.C	Make a contour plot and get the first contour in a TPolyMarker.
hist104_TH2Poly_fibonacci.C	Create a histogram representing the "Fibonacci spiral".

Graphics

Tutorial	Description
hist043_Graphics_highlight.C	Use the highlight mechanism to update the title of a histogram in real time.
hist044_Graphics_highlight2D.C	Use the highlight mechanism to displaying the X and Y projections at a bin in real time.
hist045_Graphics_highlight_ntuple.C	Use the highlight mechanism to display which events of an ntuple contribute to a bin.
hist046_Graphics_highlight1D.C	Use the highlight mechanism to zoom on a histogram.
hist047_Graphics_candle_decay.C	Candle plot illustrating a time development of a certain value.
hist048_Graphics_candle_hist.C	Illustrate candle plot options.
hist049_Graphics_candle_plot.C	Create a candle plot with 2-D histograms.
hist050_Graphics_candle_plot_options.C	Illustrate more candle plot options.
hist051_Graphics_candle_plot_stack.C	Create a THStack with candle plot option.
hist052_Graphics_candle_plot_whiskers.C	Create a candle plot showing the whiskers definition.
hist053_Graphics_candle_scaled.C	Illustrate what scaling effects on candle and violin charts.
hist054_Graphics_logscales.C	Draw parametric functions with log scales.
hist055_Graphics_xyplot.C	Draw a curve in an orthogonal axis system.

TExec

Tutorial		Description
hist057_TExec_th1.C		Echo object at mouse position.
hist058_TExec_th2.C		Echo object at mouse position and show a graphics line.
hist105_TExec_dynamic_slice.C	hist105_TExec_dynamic_slice.py	Show the slice of a TH2 following the mouse position.

Files
file	greyscale.C
	Create grey scale of 200 x 200 boxes.
file	hist000_TH1_first.C
	Hello World example for TH1.
file	hist000_TH1_first.py
	Hello World example for TH1.
file	hist001_TH1_fillrandom.C
	Fill a 1D histogram with random values using predefined functions
file	hist001_TH1_fillrandom.py
	Fill a 1D histogram with random values using predefined functions
file	hist002_TH1_fillrandom_userfunc.C
	Fill a 1D histogram from a user-defined parametric function.
file	hist002_TH1_fillrandom_userfunc.py
	Fill a 1D histogram from a user-defined parametric function.
file	hist003_TH1_draw.C
	Draw a 1D histogram to a canvas.
file	hist003_TH1_draw.py
	Draw a 1D histogram to a canvas.
file	hist004_TH1_labels.C
	1D histograms with alphanumeric labels.
file	hist005_TH1_palettecolor.C
	Palette coloring for TH1
file	hist006_TH1_bar_charts.C
	Draw 1D histograms as bar charts
file	hist007_TH1_liveupdate.C
	Histograms filled and drawn in a loop.
file	hist007_TH1_liveupdate.py
	Simple example illustrating how to use the C++ interpreter
file	hist008_TH1_zoom.C
	Changing the Range on the X-Axis of a Histogram
file	hist009_TH1_normalize.C
	Normalizing a Histogram
file	hist010_TH1_two_scales.C
	Example of macro illustrating how to superimpose two histograms with different scales in the "same" pad.
file	hist010_TH1_two_scales.py
	Example of macro illustrating how to superimpose two histograms with different scales in the "same" pad.
file	hist011_TH1_legend_autoplaced.C
	The legend can be placed automatically in the current pad in an empty space found at painting time.
file	hist012_TH1_hksimple.C
	Illustrates the advantages of a TH1K histogram
file	hist013_TH1_rebin.C
	Rebin a variable bin-width histogram.
file	hist014_TH1_cumulative.C
	Illustrate use of the TH1::GetCumulative method.
file	hist015_TH1_read_and_draw.C
	Read a 1-D histogram from a ROOT File and draw it.
file	hist015_TH1_read_and_draw.py
	A Simple histogram drawing example
file	hist016_TH1_different_scales_canvas.C
	Example of a canvas showing two histograms with different scales.
file	hist017_TH1_smooth.C
	Histogram smoothing.
file	hist018_TH2_cutg.C
	This example demonstrates how to display a 2D histogram and use TCutG object to select bins for drawing.
file	hist019_TH2_projection.C
	This example demonstrates how to display a histogram and its two projections.
file	hist020_TH2_draw.C
	Display the various 2-d drawing options
file	hist021_TH2_reverse_axis.C
	Example showing an histogram with reverse axis.
file	hist022_TH2_palette.C
	When an histogram is drawn with the option COLZ, a palette is automatically drawn vertically on the right side of the plot.
file	hist023_THStack_simple.C
	Example of stacked histograms: class THStack.
file	hist024_THStack_pads.C
	Drawing stack histograms on subpads.
file	hist025_THStack_2d_palette_color.C
	Palette coloring for 2D histograms' stack is activated thanks to the option PFC (Palette Fill Color).
file	hist026_THStack_color_scheme.C
	This example demonstrates how to use the accessible color schemes with THStack.
file	hist027_THStack_palette_color.C
	Palette coloring for histograms' stack is activated thanks to the options PFC (Palette Fill Color), PLC (Palette Line Color) and AMC (Palette Marker Color).
file	hist028_THStack_multicolor.C
	Use a THStack to show a 2-D hist with cells with different colors.
file	hist029_TRatioPlot_simple.C
	Example creating a simple ratio plot of two histograms using the pois division option.
file	hist029_TRatioPlot_simple.py
	Example creating a simple ratio plot of two histograms using the pois division option.
file	hist030_TRatioPlot_residual.C
	Example of a fit residual plot.
file	hist030_TRatioPlot_residual.py
	Example of a fit residual plot.
file	hist031_TRatioPlot_residual_fit.C
	Example which shows how you can get the graph of the lower plot and set the y axis range for it.
file	hist031_TRatioPlot_residual_fit.py
	Example which shows how you can get the graph of the lower plot and set the y axis range for it.
file	hist032_TRatioPlot_fit_lines.C
	Example that shows custom dashed lines on the lower plot, specified by a vector of floats.
file	hist032_TRatioPlot_fit_lines.py
	Example that shows custom dashed lines on the lower plot, specified by a vector of floats.
file	hist033_TRatioPlot_fit_confidence.C
	Example that shows how you can set the colors of the confidence interval bands by using the method TRatioPlot::SetConfidenceIntervalColors.
file	hist033_TRatioPlot_fit_confidence.py
	Example that shows how you can set the colors of the confidence interval bands by using the method TRatioPlot::SetConfidenceIntervalColors.
file	hist034_TRatioPlot_fit_margin.C
	Example showing a fit residual plot, where the separation margin has been set to 0.
file	hist034_TRatioPlot_fit_margin.py
	Example showing a fit residual plot, where the separation margin has been set to 0.
file	hist036_TH2_labels.C
	2-D histograms with alphanumeric labels.
file	hist037_TH2Poly_boxes.C
	This tutorial illustrates how to create an histogram with polygonal bins (TH2Poly).
file	hist038_TH2Poly_honeycomb.C
	This tutorial illustrates how to create an histogram with hexagonal bins (TH2Poly).
file	hist039_TH2Poly_usa.C
	This tutorial illustrates how to create an histogram with polygonal bins (TH2Poly), fill it and draw it using the col option.
file	hist040_TH2Poly_europe.C
	This tutorial illustrates how to create an histogram with polygonal bins (TH2Poly), fill it and draw it.
file	hist041_TProfile2Poly_realistic.C
	Different charges depending on region
file	hist042_TProfile2Poly_module_error.C
	Simulate faulty detector panel w.r.t.
file	hist043_Graphics_highlight.C
	This tutorial demonstrates how the highlight mechanism can be used on an histogram.
file	hist044_Graphics_highlight2D.C
	This tutorial demonstrates how the highlight mechanism can be used on an histogram.
file	hist045_Graphics_highlight_ntuple.C
	This tutorial demonstrates how the highlight mechanism can be used on a ntuple.
file	hist046_Graphics_highlight1D.C
	This tutorial demonstrates how the highlight mechanism can be used on an histogram.
file	hist047_Graphics_candle_decay.C
	Candle Decay, illustrate a time development of a certain value.
file	hist048_Graphics_candle_hist.C
	Example showing how to combine the various candle plot options.
file	hist049_Graphics_candle_plot.C
	Example of candle plot with 2-D histograms.
file	hist050_Graphics_candle_plot_options.C
	Example showing how to combine the various candle plot options.
file	hist051_Graphics_candle_plot_stack.C
	Example showing how a THStack with candle plot option.
file	hist052_Graphics_candle_plot_whiskers.C
	Example of candle plot showing the whiskers definition.
file	hist053_Graphics_candle_scaled.C
	Candle Scaled, illustrates what scaling does on candle and violin charts.
file	hist054_Graphics_logscales.C
	Draw parametric functions with log scales.
file	hist055_Graphics_xyplot.C
	Example showing how to produce a plot with an orthogonal axis system centered at (0,0).
file	hist056_TPolyMarker_contour.C
	Make a contour plot and get the first contour in a TPolyMarker.
file	hist057_TExec_th1.C
	Echo object at mouse position.
file	hist058_TExec_th2.C
	Echo object at mouse position and show a graphics line.
file	hist060_TH1_Stats.C
	Edit statistics box.
file	hist101_TH1_autobinning.C
	Fill multiple histograms with different functions and automatic binning.
file	hist102_TH2_contour_list.C
	Getting Contours From TH2D.
file	hist103_THnSparse_hist.C
	Evaluate the performance of THnSparse vs TH1/2/3/nF for different numbers of dimensions and bins per dimension.
file	hist104_TH2Poly_fibonacci.C
	A TH2Poly build with Fibonacci numbers.
file	hist105_TExec_dynamic_slice.C
	Show the slice of a TH2 following the mouse position.
file	hist105_TExec_dynamic_slice.py
	Example of function called when a mouse event occurs in a pad.