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root:pyroot_th1 [2017/06/22 12:05] – [Filling a histogram] iwnroot:pyroot_th1 [2017/09/01 16:26] – iwn
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 +[[root:root|Getting started with ROOT]] -> [[root:pyroot|Useful pyROOT snippets]] → [[root:pyroot_th1|Handling TH1 histograms]]
 +
 ====== Handling TH1 histograms ====== ====== Handling TH1 histograms ======
  
-To use ''TH1D'' in ''python'', you can either do+===== Importing ROOT classes ===== 
 + 
 +To use ''TH1D'' in ''python'', you can either only import a ''TH1D'' class:
 <code python> <code python>
 from ROOT import TH1D from ROOT import TH1D
 hist = TH1D("hist_name","hist_title",100,0,100) hist = TH1D("hist_name","hist_title",100,0,100)
 </code> </code>
-or+or //all// classes:
 <code python> <code python>
 from ROOT import * # loads all classes, and thus takes longer from ROOT import * # loads all classes, and thus takes longer
 hist = TH1D("hist_name","hist_title",100,0,100) hist = TH1D("hist_name","hist_title",100,0,100)
 </code> </code>
-or+or only the ''ROOT'' module:
 <code python> <code python>
 import ROOT import ROOT
Line 17: Line 21:
 </code> </code>
 The examples below also make use of ''ROOT'''s ''gRandom'' to make some random variables. The examples below also make use of ''ROOT'''s ''gRandom'' to make some random variables.
- 
 ===== Filling a histogram ===== ===== Filling a histogram =====
  
Line 23: Line 26:
  
 <code python> <code python>
-from ROOT import TH1D, gRandom 
 hist = TH1D("hist_name","hist title",100,0,100) hist = TH1D("hist_name","hist title",100,0,100)
 for i in xrange(10000): for i in xrange(10000):
Line 37: Line 39:
 ===== Filling a histogram from a tree ===== ===== Filling a histogram from a tree =====
  
-The classic way would be+The classic way would be with a simple for loop
 <code python> <code python>
 hist = TH1D("hist_name","hist title",100,0,100) hist = TH1D("hist_name","hist title",100,0,100)
Line 51: Line 53:
 Note that the histogram has been saved into ''ROOT'''s working memory and is therefore accessible via its name in the ''Draw'' function, ''"hist_name"'' in this example. Note that the histogram has been saved into ''ROOT'''s working memory and is therefore accessible via its name in the ''Draw'' function, ''"hist_name"'' in this example.
  
-You can also use mathematical expressions, including boolean expressions (which can take the value ''0.0'' or ''1.0''):+You can also use **mathematical expressions**, including **boolean expressions** (which can take the value ''0.0'' or ''1.0''):
 <code python> <code python>
 tree.Draw("2*sqrt(px*px+py*py) >> hist_name") tree.Draw("2*sqrt(px*px+py*py) >> hist_name")
 tree.Draw("abs(eta) >> hist_name") tree.Draw("abs(eta) >> hist_name")
 tree.Draw("pt1*(eta1<2.4) + pt2*(eta2<2.4) >> hist_name") # boolean expressions tree.Draw("pt1*(eta1<2.4) + pt2*(eta2<2.4) >> hist_name") # boolean expressions
 +</code>
 +This also includes custom functions, which you can load into ''ROOT'' with a ''C'' file:
 +<code python>
 +from ROOT import gROOT, ...
 +gROOT.Macro("myfunctions.C+")
 +...
 +tree.Draw("deltaR(eta1,phi1,eta2,phi2) >> hist_name")    # deltaR     function defined in "myfunctions.C+"
 +tree.Draw("pt1 >> hist_name","(pt>30)*weightEta1(eta1)") # weightEta1 function defined in "myfunctions.C+"
 </code> </code>
  
-You can apply some selections using variable, available in the tree's branches:+You can apply some **selections** using variable, available in the tree's branches:
 <code python> <code python>
 tree.Draw("px >> hist_name","pt>20 && E>20") tree.Draw("px >> hist_name","pt>20 && E>20")
 </code> </code>
  
-You can apply some selections and/or a weight, if a weight variable is available in the tree:+You can apply some selections and/or a **weight**, if a weight variable is available in the tree:
 <code python> <code python>
-tree.Draw("px >> hist_name","(pt>20 && E>20)*weight") 
 tree.Draw("px >> hist_name","weight") tree.Draw("px >> hist_name","weight")
 +tree.Draw("px >> hist_name","(pt>20 && E>20)*weight")
 </code> </code>
  
Line 77: Line 87:
 </code> </code>
  
-It's also possible to pass some option you would normally use in "TH1::Draw()". It is passed as the third string.+It's also possible to pass some **draw option** you would normally use in "TH1::Draw()". It is passed as the third string.
 <code python> <code python>
 tree.Draw("px >> h1(100,0,100)","","E2") tree.Draw("px >> h1(100,0,100)","","E2")
Line 92: Line 102:
 [2] tree->Draw("px >> h1(100,0,100)","pt>20") [2] tree->Draw("px >> h1(100,0,100)","pt>20")
 [3] tree->Draw("px >> h1(100,0,100)","","E2") [3] tree->Draw("px >> h1(100,0,100)","","E2")
-[4] tree->Draw("py >> h2(100,0,100)","","E2 SAME")+[4] tree->Draw("py >> h2(100,0,100)","","E2 SAME") // compare to px
 </code> </code>
root/pyroot_th1.txt · Last modified: 2017/09/05 10:35 by iwn

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