TTreeDraw

TTreeDraw is a feature of the ROOT data analysis framework used to visualize data stored in a TTree. It provides rapid, inline plotting of expressions and variable combinations without separate histogramming steps, making it a common tool for exploratory data analysis in high-energy physics.

Usage is through the TTree::Draw method, with the general syntax: tree->Draw("expression","selection","drawOptions"). The expression can be a single variable, a mathematical expression, or a pair of variables separated by a colon for a 2D plot. If the expression contains an output specification like >>histName(bins,xmin,xmax), ROOT creates or fills a histogram named histName. When no such specification is provided, the result is drawn directly in the current pad.

Examples: t->Draw("energy"); t->Draw("pt:eta","pt>1","COLZ"); t->Draw("nTracks>>trkHist(60,0,60)","abs(charge)==1","goff").

Options in drawOptions control rendering and behavior. Common elements are goff (suppress on-screen drawing), same (overlay on the current pad), and style keywords such as hist (draw as a histogram) or colz (colorize 2D histograms).

Limitations and tips: TTree::Draw operates best on compact expressions and is not a full replacement for dedicated histogramming or data processing. For large trees, consider using goff and post-processing, or switch to TTreeReader or the ROOT RDataFrame for efficient iteration and lazy evaluation.

See also: TTree, TH1, TH2, ROOT, TTreeReader, RDataFrame.