demarches-normaliennes/lib/core_ext/array.rb

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# Adapted from https://github.com/thirtysixthspan/descriptive_statistics
# Copyright (c) 2010-2014 Derrick Parkhurst (derrick.parkhurst@gmail.com)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
class Array
def percentile(p)
values = self.sort
if values.empty?
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return 0
elsif values.size == 1
return values.first
elsif p == 100
return values.last
end
rank = p / 100.0 * (values.size - 1)
lower, upper = values[rank.floor, 2]
lower + (upper - lower) * (rank - rank.floor)
end
end