class description - source file - inheritance tree

class TH1F : public TH1, public TArrayF

TH1F TH1F() TH1F TH1F(const char* name, const char* title, Int_t nbinsx, Axis_t xlow, Axis_t xup) TH1F TH1F(const char* name, const char* title, Int_t nbinsx, const Float_t* xbins) TH1F TH1F(const char* name, const char* title, Int_t nbinsx, const Double_t* xbins) TH1F TH1F(const TVector& v) TH1F TH1F(const TH1F& h1f) virtual void ~TH1F() virtual void AddBinContent(Int_t bin) virtual void AddBinContent(Int_t bin, Stat_t w) static TClass* Class() virtual void Copy(TObject& hnew) virtual TH1* DrawCopy(Option_t* option) virtual Stat_t GetBinContent(Int_t bin) const virtual Stat_t GetBinContent(Int_t bin, Int_t) const virtual Stat_t GetBinContent(Int_t bin, Int_t, Int_t) const virtual TClass* IsA() const TH1F& operator=(const TH1F& h1) virtual void Reset(Option_t* option) virtual void SetBinContent(Int_t bin, Stat_t content) virtual void SetBinContent(Int_t bin, Int_t, Stat_t content) virtual void SetBinContent(Int_t bin, Int_t, Int_t, Stat_t content) virtual void SetBinsLength(Int_t n = -1) virtual void ShowMembers(TMemberInspector& insp, char* parent) virtual void Streamer(TBuffer& b) void StreamerNVirtual(TBuffer& b)

Data Members

Class Description

                     The H I S T O G R A M   Classes

     ROOT supports the following histogram types:

      1-D histograms:
         TH1C : histograms with one byte per channel.   Maximum bin content = 255
         TH1S : histograms with one short per channel.  Maximum bin content = 65535
         TH1F : histograms with one float per channel.  Maximum precision 7 digits
         TH1D : histograms with one double per channel. Maximum precision 14 digits

      2-D histograms:
         TH2C : histograms with one byte per channel.   Maximum bin content = 255
         TH2S : histograms with one short per channel.  Maximum bin content = 65535
         TH2F : histograms with one float per channel.  Maximum precision 7 digits
         TH2D : histograms with one double per channel. Maximum precision 14 digits

      3-D histograms:
         TH3C : histograms with one byte per channel.   Maximum bin content = 255
         TH3S : histograms with one short per channel.  Maximum bin content = 65535
         TH3F : histograms with one float per channel.  Maximum precision 7 digits
         TH3D : histograms with one double per channel. Maximum precision 14 digits

      Profile histograms: See classes  TProfile and TProfile2D
      Profile histograms are used to display the mean value of Y and its RMS
      for each bin in X. Profile histograms are in many cases an elegant
      replacement of two-dimensional histograms : the inter-relation of two
      measured quantities X and Y can always be visualized by a two-dimensional
      histogram or scatter-plot; If Y is an unknown (but single-valued)
      approximate function of X, this function is displayed by a profile
      histogram with much better precision than by a scatter-plot.

   - All histogram classes are derived from the base class TH1

                |                |       |      |      |     |
                |                |      TH1C   TH1S   TH1F  TH1D
                |                |                           |
                |                |                           |
                |               TH2                      TProfile
                |                |
                |                |
                |                -----------------------------
                |                        |      |      |     |
                |                       TH2C   TH2S   TH2F  TH2D
                |                                            |
               TH3                                           |
                |                                        TProfile2D
                        |      |      |      |
                       TH3C   TH3S   TH3F   TH3D

      The TH*C classes also inherit from the array class TArrayC.
      The TH*S classes also inherit from the array class TArrayS.
      The TH*F classes also inherit from the array class TArrayF.
      The TH*D classes also inherit from the array class TArrayD.

     Creating histograms
     Histograms are created by invoking one of the constructors, eg
       TH1F *h1 = new TH1F("h1","h1 title",100,0,4.4);
       TH2F *h2 = new TH2F("h2","h2 title",40,0,4,30,-3,3);
     histograms may also be created by:
       - calling the Clone function, see below
       - making a projection from a 2-D or 3-D histogram, see below
       - reading an histogram from a file
     When an histogram is created, a reference to it is automatically added
     to the list of in-memory objects for the current file or directory.
     This default behaviour can be changed by:
       h->SetDirectory(0);         // for the current histogram h
       TH1::AddDirectory(kFALSE);  // sets a global switch disabling the reference
     When the histogram is deleted, the reference to it is removed from
     the list of objects in memory.
     When a file is closed, all histograms in memory associated with this file
     are automatically deleted.

      Fix or variable bin size

     All histogram types support either fix or variable bin sizes.
     2-D histograms may have fix size bins along X and variable size bins
     along Y or vice-versa. The functions to fill, manipulate, draw or access
     histograms are identical in both cases.
     Each histogram always contains 3 objects TAxis: fXaxis, fYaxis and fZaxis
     To access the axis parameters, do:
        TAxis *xaxis = h->GetXaxis(); etc.
        Double_t binCenter = xaxis->GetBinCenter(bin), etc.
     See class TAxis for a description of all the access functions.
     The axis range is always stored internally in double precision.

      Convention for numbering bins
      For all histogram types: nbins, xlow, xup
        bin = 0;       underflow bin
        bin = 1;       first bin with low-edge xlow INCLUDED
        bin = nbins;   last bin with upper-edge xup EXCLUDED
        bin = nbins+1; overflow bin
      In case of 2-D or 3-D histograms, a "global bin" number is defined.
      For example, assuming a 3-D histogram with binx,biny,binz, the function
        Int_t bin = h->GetBin(binx,biny,binz);
      returns a global/linearized bin number. This global bin is useful
      to access the bin information independently of the dimension.

     Alphanumeric Bin Labels
     By default, an histogram axis is drawn with its numeric bin labels.
     One can specify alphanumeric labels instead with:
        1- call TAxis::SetBinLabel(bin,label);
           This can always be done before or after filling.
           When the histogram is drawn, bin labels will be automatically drawn.
           See example in $ROOTSYS/tutorials/labels1.C, labels2.C
        2- call to a Fill function with one of the arguments being a string, eg
           See example in $ROOTSYS/tutorials/hlabels1.C, hlabels2.C
        3- via TTree::Draw.
           see for example $ROOTSYS/tutorials/cern.C
           tree.Draw("Nation::Division"); where "Nation" and "Division"
           are two branches of a Tree.
     When using the options 2 or 3 above, the labels are automatically
     added to the list (THashList) of labels for a given axis.
     By default, an axis is drawn with the order of bins corresponding
     to the filling sequence. It is possible to reorder the axis
       - alphabetically
       - by increasing or decreasing values
     The reordering can be triggered via the TAxis contextMenu by selecting
     the menu item "LabelsOption" or by calling directly
        TH1::LabelsOption(option,axis) where
          -axis may be "X","Y" or "Z"
          -option may be:
           option = "a" sort by alphabetic order
                  = ">" sort by decreasing values
                  = "<" sort by increasing values
                  = "h" draw labels horizonthal
                  = "v" draw labels vertical
                  = "u" draw labels up (end of label right adjusted)
                  = "d" draw labels down (start of label left adjusted)

     When using the option 2 above, new labels are added by doubling the current
     number of bins in case one label does not exist yet.
     When the Filling is terminated, it is possible to trim the number
     of bins to match the number of active labels by calling
           TH1::LabelsDeflate(axis) with axis = "X","Y" or "Z"
     This operation is automatic when using TTree::Draw.
     Once bin labels have been created, they become persistent if the histogram
     is written to a file or when generating the C++ code via SavePrimitive.

     Histograms with automatic bins
     When an histogram is created with an axis lower limit greater or equal
     to its upper limit, the SetBuffer is automatically called with an
     argument fBufferSize equal to fgBufferSize (default value=1000).
     fgBufferSize may be reset via the static function TH1::SetDefaultBufferSize.
     The axis limits will be automatically computed when the buffer will
     be full or when the function BufferEmpty is called.

     Filling histograms
     An histogram is typically filled with statements like:
       h1->Fill(x,w); //fill with weight
     or via one of the Fill functions accepting names described above.
     The Fill functions compute the bin number corresponding to the given
     x,y or z argument and increment this bin by the given weight.
     The Fill functions return the bin number for 1-D histograms or global
     bin number for 2-D and 3-D histograms.
     If TH1::Sumw2 has been called before filling, the sum of squares of
     weights is also stored.
     One can also increment directly a bin number via TH1::AddBinContent
     or replace the existing content via TH1::SetBinContent.
     To access the bin content of a given bin, do:
       Double_t binContent = h->GetBinContent(bin);

     By default, the bin number is computed using the current axis ranges.
     If the automatic binning option has been set via
     then, the Fill Function will automatically extend the axis range to
     accomodate the new value specified in the Fill argument. The method
     used is to double the bin size until the new value fits in the range,
     merging bins two by two. This automatic binning options is extensively
     used by the TTree::Draw function when histogramming Tree variables
     with an unknown range.
     This automatic binning option is supported for 1-d, 2-D and 3-D histograms.

     During filling, some statistics parameters are incremented to compute
     the mean value and Root Mean Square with the maximum precision.

     In case of histograms of type TH1C, TH1S, TH2C, TH2S, TH3C, TH3S
     a check is made that the bin contents do not exceed the maximum positive
     capacity (127 or 65535). Histograms of all types may have positive
     or/and negative bin contents.

     At any time, an histogram can be rebinned via TH1::Rebin. This function
     returns a new histogram with the rebinned contents.
     If bin errors were stored, they are recomputed during the rebinning.

     Associated errors
     By default, for each bin, the sum of weights is computed at fill time.
     One can also call TH1::Sumw2 to force the storage and computation
     of the sum of the square of weights per bin.
     If Sumw2 has been called, the error per bin is computed as the
     sqrt(sum of squares of weights), otherwise the error is set equal
     to the sqrt(bin content).
     To return the error for a given bin number, do:
        Double_t error = h->GetBinError(bin);

     Associated functions
     One or more object (typically a TF1*) can be added to the list
     of functions (fFunctions) associated to each histogram.
     When TH1::Fit is invoked, the fitted function is added to this list.
     Given an histogram h, one can retrieve an associated function
     with:  TF1 *myfunc = h->GetFunction("myfunc");

     Operations on histograms

     Many types of operations are supported on histograms or between histograms
     - Addition of an histogram to the current histogram
     - Additions of two histograms with coefficients and storage into the current
     - Multiplications and Divisions are supported in the same way as additions.
     - The Add, Divide and Multiply functions also exist to add,divide or multiply
       an histogram by a function.
     If an histogram has associated error bars (TH1::Sumw2 has been called),
     the resulting error bars are also computed assuming independent histograms.
     In case of divisions, Binomial errors are also supported.

     Fitting histograms

     Histograms (1-D,2-D,3-D and Profiles) can be fitted with a user
     specified function via TH1::Fit. When an histogram is fitted, the
     resulting function with its parameters is added to the list of functions
     of this histogram. If the histogram is made persistent, the list of
     associated functions is also persistent. Given a pointer (see above)
     to an associated function myfunc, one can retrieve the function/fit
     parameters with calls such as:
       Double_t chi2 = myfunc->GetChisquare();
       Double_t par0 = myfunc->GetParameter(0); //value of 1st parameter
       Double_t err0 = myfunc->GetParError(0);  //error on first parameter

     Projections of histograms
     One can:
      - make a 1-D projection of a 2-D histogram or Profile
        see functions TH2::ProjectionX,Y, TH2::ProfileX,Y, TProfile::ProjectionX
      - make a 1-D, 2-D or profile out of a 3-D histogram
        see functions TH3::ProjectionZ, TH3::Project3D.

     One can fit these projections via:
      TH2::FitSlicesX,Y, TH3::FitSlicesZ.

     Random Numbers and histograms
     TH1::FillRandom can be used to randomly fill an histogram using
                    the contents of an existing TF1 function or another
                    TH1 histogram (for all dimensions).
     For example the following two statements create and fill an histogram
     10000 times with a default gaussian distribution of mean 0 and sigma 1:
       TH1F h1("h1","histo from a gaussian",100,-3,3);
     TH1::GetRandom can be used to return a random number distributed
                    according the contents of an histogram.

     Making a copy of an histogram
     Like for any other Root object derived from TObject, one can use
     the Clone function. This makes an identical copy of the original histogram
     including all associated errors and functions, eg:
       TH1F *hnew = (TH1F*)h->Clone();
       hnew->SetName("hnew"); //recommended, otherwise you get 2 histograms
                              //with the same name

     Normalizing histograms
     One can scale an histogram such that the bins integral is equal to
     to the normalization parameter via TH1::Scale(Double_t norm);

     Drawing histograms
     Histograms are drawn via the THistPainter class. Each histogram has
     a pointer to its own painter (to be usable in a multithreaded program).
     Many drawing options are supported.
     See THistPainter::Paint for more details.
     The same histogram can be drawn with different options in different pads.
     When an histogram drawn in a pad is deleted, the histogram is
     automatically removed from the pad or pads where it was drawn.
     If an histogram is drawn in a pad, then filled again, the new status
     of the histogram will be automatically shown in the pad next time
     the pad is updated. One does not need to redraw the histogram.
     To draw the current version of an histogram in a pad, one can use
     This makes a clone (see Clone below) of the histogram. Once the clone
     is drawn, the original histogram may be modified or deleted without
     affecting the aspect of the clone.

     One can use TH1::SetMaximum and TH1::SetMinimum to force a particular
     value for the maximum or the minimum scale on the plot.

     TH1::UseCurrentStyle can be used to change all histogram graphics
     attributes to correspond to the current selected style.
     This function must be called for each histogram.
     In case one reads and draws many histograms from a file, one can force
     the histograms to inherit automatically the current graphics style
     by calling before gROOT->ForceStyle();

     Setting Drawing histogram contour levels (2-D hists only)
     By default contours are automatically generated at equidistant
     intervals. A default value of 20 levels is used. This can be modified
     via TH1::SetContour or TH1::SetContourLevel.
     the contours level info is used by the drawing options "cont", "surf",
     and "lego".

     Setting histogram graphics attributes
     The histogram classes inherit from the attribute classes:
       TAttLine, TAttFill, TAttMarker and TAttText.
     See the member functions of these classes for the list of options.

     Giving titles to the X, Y and Z axis
       h->GetXaxis()->SetTitle("X axis title");
       h->GetYaxis()->SetTitle("Y axis title");
     The histogram title and the axis titles can be any TLatex string.
     The titles are part of the persistent histogram.

     Saving/Reading histograms to/from a Root file
     The following statements create a Root file and store an histogram
     on the file. Because TH1 derives from TNamed, the key identifier on
     the file is the histogram name:
        TFile f("histos.root","new");
        TH1F h1("hgaus","histo from a gaussian",100,-3,3);
     To Read this histogram in another Root session, do:
        TFile f("histos.root");
        TH1F *h = (TH1F*)f.Get("hgaus");
     One can save all histograms in memory to the file by:

     Miscelaneous operations

      TH1::KolmogorovTest: Statistical test of compatibility in shape between
                           two histograms.
      TH1::Smooth smooths the bin contents of a 1-d histogram
      TH1::Integral returns the integral of bin contents in a given bin range
      TH1::GetMean(int axis) returns the mean value along axis
      TH1::GetRMS(int axis)  returns the Root Mean Square along axis
      TH1::GetEntries returns the number of entries
      TH1::Reset() resets the bin contents and errors of an histogram.




TH1F(): TH1(), TArrayF()

TH1F(const char *name,const char *title,Int_t nbins,Axis_t xlow,Axis_t xup) : TH1(name,title,nbins,xlow,xup)
    Create a 1-Dim histogram with fix bins of type float
           (see TH1::TH1 for explanation of parameters)

TH1F(const char *name,const char *title,Int_t nbins,const Float_t *xbins) : TH1(name,title,nbins,xbins)
    Create a 1-Dim histogram with variable bins of type float
           (see TH1::TH1 for explanation of parameters)

TH1F(const char *name,const char *title,Int_t nbins,const Double_t *xbins) : TH1(name,title,nbins,xbins)
    Create a 1-Dim histogram with variable bins of type float
           (see TH1::TH1 for explanation of parameters)

TH1F(const TVector &v) : TH1("TVector","",v.GetNrows(),0,v.GetNrows())
 Create a histogram from a TVector
 by default the histogram name is "TVector" and title = ""

TH1F(const TH1F &h) : TH1(), TArrayF()


void Copy(TObject &newth1)

TH1* DrawCopy(Option_t *option)

Stat_t GetBinContent(Int_t bin) const

void Reset(Option_t *option)

void SetBinContent(Int_t bin, Stat_t content)
 Set bin content
 In case the bin number is greater than the number of bins and
 the timedisplay option is set or the kCanRebin bit is set,
 the number of bins is automatically doubled to accomodate the new bin

void SetBinsLength(Int_t n)
 Set total number of bins including under/overflow
 Reallocate bin contents array

Inline Functions

               void AddBinContent(Int_t bin)
               void AddBinContent(Int_t bin, Stat_t w)
             Stat_t GetBinContent(Int_t bin, Int_t) const
             Stat_t GetBinContent(Int_t bin, Int_t, Int_t) const
               void SetBinContent(Int_t bin, Int_t, Stat_t content)
               void SetBinContent(Int_t bin, Int_t, Int_t, Stat_t content)
              TH1F& operator=(const TH1F& h1)
            TClass* Class()
            TClass* IsA() const
               void ShowMembers(TMemberInspector& insp, char* parent)
               void Streamer(TBuffer& b)
               void StreamerNVirtual(TBuffer& b)

Author: Rene Brun 26/12/94
Last update: root/hist:$Name: $:$Id: TH1.cxx,v 1.109 2002/09/17 08:31:47 brun Exp $
Copyright (C) 1995-2000, Rene Brun and Fons Rademakers. *

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