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histogram Class Reference

Support for calculating histograms. More...

#include <histogram.h>

List of all members.

Public Methods
	histogram ()
	~histogram ()
void	calculate (const double *raw_data, const size_t N, bin_vec &binz)
	Calculate a histogram. More...
Private Methods
	histogram (const histogram &rhs)
void	init_bins (bin_vec &bins, const double min, const double max)
	Initialize the histogram bin array. More...

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Detailed Description

Support for calculating histograms.

The histogram class constructor is initialized with the number of bins to be used in the histogram.

Each bin is a histo_bin object which contains information on the start and end value of the bin range and the frequency in the bin. The frequency is the number of values in the data set which are greater than or equal to start and less than end.

Example:

Given an array of 20 double values, calculate the histogram. The data does not need to be in sorted order. The histogram calculation will sort it. A vector of histo_bin objects is allocated by the histogram::bin_vec class constructor. The data, number of elements in the data set and the vector of histogram bins is passed to the histogram calculate function. This will initialize each of the histogram bins with a start, end and frequency.

    const size_t num_bins = 20;
    histogram::bin_vec binz( num_bins );
    histogram histo;

    histo.calculate( data, N, binz );

    for (size_t i = 0; i < num_bins; i++) {
      size_t freq = static_cast<size_t>( binz[i] );
      printf("7.4f 2d\n", binz.start(i), freq );
    }

Note that binz[i] returns the frequency as a double, which is cast to a size_t value.

Definition at line 45 of file histogram.h.

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Constructor & Destructor Documentation

histogram::histogram ( const histogram & rhs ) [private]

histogram::histogram ( ) [inline]

Definition at line 202 of file histogram.h. {}

histogram::~histogram ( ) [inline]

Definition at line 203 of file histogram.h. {}

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Member Function Documentation

void histogram::calculate ( const double * raw_data, const size_t N, bin_vec & bins )

Calculate a histogram. Parameters: raw_data   The raw data from which to calculate the histogram N   The number of data values in raw_data bins   An array of histo_bin objects num_bins   The number of histogram bins (number of elements in histo_bin) Definition at line 52 of file histogram.cpp. Referenced by pdf::pdf_stddev(). { double *sort_data = new double[ N ]; for (size_t i = 0; i < N; i++) { sort_data[i] = raw_data[i]; } dbl_sort s; s.sort( sort_data, N ); double min = sort_data[0]; double max = sort_data[N-1]; size_t num_bins = bins.length(); init_bins( bins, min, max ); value_pool pool( sort_data, N ); size_t bin_ix = 0; double val; bool more_values = pool.get_val( val ); double end = bins.end(bin_ix); while (bin_ix < num_bins && more_values) { if (val < end) { bins[bin_ix] = bins[bin_ix] + 1; // increment the frequency more_values = pool.get_val( val ); } else { bin_ix++; end = bins.end(bin_ix); } } // while delete [] sort_data; } // calculate

void histogram::init_bins ( bin_vec & bins, const double min, const double max ) [private]

Initialize the histogram bin array. Definition at line 11 of file histogram.cpp. Referenced by calculate(). { size_t num_bins = bins.length(); double range = max - min; double bin_size = range / static_cast<double>( num_bins ); double start = min; double end = min + bin_size; for (size_t i = 0; i < num_bins; i++) { bins[i] = 0; // initialize frequency to zero bins.start(i, start ); // initialize the i'th bin start value bins.end(i, end ); // initialize the i'th bin end value start = end; end = end + bin_size; } // The frequency in a bin is incremented if a value v is // in the range start <= v < end. This is fine until // we reach the last bin, which should also get values // which are in the range start <= v <= end. So add a // small amount to the end value to assure that the // end value of the last bin is beyond the value range. bins.end(num_bins-1, bins.end(num_bins-1) + (bin_size / 10.0) ); } // init_bins

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The documentation for this class was generated from the following files:

• histogram.h
• histogram.cpp

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