Method: Histogram#number_of_bins

Defined in:
lib/histogram.rb

#number_of_bins(methd = DEFAULT_BIN_METHOD, quartile_method = DEFAULT_QUARTILE_METHOD) ⇒ Object

returns(integer) takes :scott|:sturges|:fd|:middle

middle is the median between the other three values

Note: always returns 1 if all values are the same.

inspired by Richard Cotton’s matlab implementation and the histogram page on wikipedia



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# File 'lib/histogram.rb', line 97

def number_of_bins(methd=DEFAULT_BIN_METHOD, quartile_method=DEFAULT_QUARTILE_METHOD)
  return 1 if self.to_a.uniq.size == 1

  if methd == :middle
    [:scott, :sturges, :fd].map {|v| number_of_bins(v) }.sort[1]
  else
    nbins =
      case methd
      when :scott
        range = (self.max - self.min).to_f
        (mean, stddev) = Histogram.sample_stats(self)
        if stddev == 0.0
          1
        else
          range / ( 3.5*stddev*(self.size**(-1.0/3)) )
        end
      when :sturges
        1 + Math::log2(self.size)
      when :fd
        2 * Histogram.iqrange(self, :method => quartile_method) * (self.size**(-1.0/3))
      end
    if nbins > self.size || nbins.to_f.nan? || nbins <= 0
      nbins = 1
    end
    nbins.ceil.to_i
  end
end