class Array
	def sum
		inject(nil) {|sum,x|
			sum ? sum+x : x
		}
	end
	def mean
		sum/size
	end

	def stddev
		std = 0
		res = 0
		devs = []
		self.each { |x|
			devs.push(x - mean)
		}
		devs.each {|y|
			res = res + y**2
		}
		Math.sqrt(res/(size-1))
	end

	def median
		self.sort!
		res = (0.5*(self.size+1))
		if res.ceil != res.floor
			retr = ((self[res.ceil-1]+self[res.floor-1])/2.0)
		else
			retr = self[res]
		end
		retr
	end

	def q1
		self.sort!
		retr = 0
		res = (0.25*(self.size+1))
		if res.ceil != res.floor
			retr = ((self[res.ceil-1] + self[res.floor-1])/2.0)
		else
			retr = self[res]
		end

		retr
	end

	def q3
	  self.sort!
        retr = 0
        res = (0.75*(self.size+1))
        if res.ceil != res.floor
            retr = ((self[res.ceil-1] + self[res.floor-1])/2.0)
        else
            retr = self[res]
        end
        retr
	end

	def iqr
		q3-q1
	end
end