Stuff that might be useful when working with ROOT

Some of the following got posted to roottalk in the past. Some was lying around in the old tutorials. Some was provided by users. Some was taken from user support mails. Some might be wrong, please complain if you find examples that don't work in your preferred version of ROOT.

Some of the macros given below need input, most often hsimple.root (which you get by executing the 'hsimple' demo -- try .x hsimple.C).

Histograms	Plot TH1 in directory	Draw a TH1 that is in a subdirectory of a ROOT file
	Two Stats boxes	Draw a second statistics box (when overlaying histograms)
	No Histogram Title	Get rid of the histogram title box
	Rotated Histogram	A function to draw a TH1 rotated by 90 degrees. (needs hsimple.root) picture
	Rotated Histograms II	Draw a 2-d plot and the projections on top and side (needs hsimple.root) picture
	Merge rootfiles with histograms	Small executable to merge histograms in different rootfiles (needs Makefile)
	Fill histogram into arrays	Works for both 1-d and 2-d histograms
	h/get_vect/cont	Plot two 1-d histograms against each other picture
Trees	Copy trees	Copy a tree from one file to another
	Merge rootfiles with trees	Small executable to merge trees in different root files (needs Makefile)
	Scan trees	Print Variables of a tree (and select events in that tree)
	Write subset of tree into file	Uses TEventList to copy tree entries
	Fit two ntuple columns	Do you know how to do this in PAW? (needs hsimple.root)
	2d arrays in trees	With 'optimal' packing
	Display of 2 trees	How to make a scatter plot of variables from different trees
	Reduce number of variables	Copy part of the variables of a tree into another file
	Enhanced subset of tree	Take a tree, dump a few of its variables and new variables into a new tree
	Draw all branches	Loop over all branches of a tree and draw their variable
Graphics	Custom Colors	Define your own colors
	LEP-style plots	How to create world-average, checks, ... plots picture
	No red box	Remove the red box around your pad/canvas
	PAW-like style	Get a better style than the default
	Overlay two graphs	Overlay two graphs with a different scale picture
	Axis labelling	Rotate long bin labels picture
Fitting	Goodness of fit	Get chi2 and ndof
	Constant + double Gaussian	How to define a non-trivial function and fit interactively
	Minuit: error matrix	How to display the error matrix plot and txt
	Minuit: Error and correlation matrix	How to access internal parameters of Minuit
	Fit a TH1+TF1 to a TH1	Using a combination of function and histogram in a fit to a histogram picture
	Fit a TH2D in slices	Slice a 2-d histogram and fit a function to all slices
	Fit with 'discontinuous' function	Fit histogram with function having gaps picture
Functions	Splines	Use splines to interpolate a graph picture
	Draw Integral	Given f(t,S), draw the integral F(S) = I_t1^t2 f(t,S) dt as a function of S
	Piece-wise function	Define a function with f(x) for x < x1 and g(x) for x > x1 picture
	Improve function drawing	Use more points for the interpolation during function drawing
	Predefined function definition	Define functions with built-in functions
	User function definition	Define functions in a separate file
	Function drawing	Some options useful for function drawing
Miscellaneous	Invoke one macro from another	How to execute '.x' a macro from another macro
	Loop over all histograms	Loop over all histograms in a file and draw them
	Decouple histogram from file	Read a histogram from a file and close the file afterwards
	Reading data files	Read in many files in a directory (C++ style)
	Opening all rootfiles in a directory	Read in many files in a directory (C-Style)
	Write TH1 to file	Save a TH1 from one ROOT file into another ROOT file
	Wait between plots	GUI and keyboard-driven examples how to wait between plots
	Macro for interactive and compiled use	Skeleton for a macro with necessary #ifdef's for CINT

If you have a macro or function that you find very useful, please consider contributing it to this page.