class Array

# File lib/statistiks/array/mean.rb, line 2
def mean(round = 5)
  (self.sum.to_f/self.length).round(round)
end

# File lib/statistiks/array/percentile.rb, line 10
def median
  self.percentile(50)
end

# File lib/statistiks/array/percentile.rb, line 2
def percentile(p)
  if p < 0 || p > 100
    nil
  else
    self.sort[((p.to_f / 100.0) * self.length.to_f) - 0.5]
  end
end

# File lib/statistiks/array/percentile.rb, line 14
def quartiles
      [self.percentile(25), self.percentile(50), self.percentile(75)]
end

# File lib/statistiks/array/sd.rb, line 2
def sd(round = 5)
  Math.sqrt(self.variance).round(round)
end

# File lib/statistiks/array/sum.rb, line 2
def sum(round = 5)
  self.inject(:+).round(round)
end

# File lib/statistiks/array/variance.rb, line 2
def variance(round = 5)
  mean = self.mean
      ((1.0/(self.length - 1))*self.map{ |x| (x - mean)**2 }.sum).round(round)
end