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| -rw-r--r-- | enum.c | 45 |
1 files changed, 45 insertions, 0 deletions
@@ -1777,6 +1777,51 @@ max_by_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, args)) * * a = %w[albatross dog horse] * a.max_by(2) {|x| x.length } #=> ["horse", "albatross"] + * + * enum.max_by(n) can be used to implement weighted random sampling. + * Following example implements and use Enumerable#wsample. + * + * module Enumerable + * # weighted random sampling. + * # + * # Pavlos S. Efraimidis, Paul G. Spirakis + * # Weighted random sampling with a reservoir + * # Information Processing Letters + * # Volume 97, Issue 5 (16 March 2006) + * def wsample(n) + * self.max_by(n) {|v| rand ** (1.0/yield(v)) } + * end + * end + * e = (-20..20).to_a*10000 + * a = e.wsample(20000) {|x| + * Math.exp(-(x/5.0)**2) # normal distribution + * } + * # a is 20000 samples from e. + * p a.length #=> 20000 + * h = a.group_by {|x| x } + * -10.upto(10) {|x| puts "*" * (h[x].length/30.0).to_i if h[x] } + * #=> * + * # *** + * # ****** + * # *********** + * # ****************** + * # ***************************** + * # ***************************************** + * # **************************************************** + * # *************************************************************** + * # ******************************************************************** + * # *********************************************************************** + * # *********************************************************************** + * # ************************************************************** + * # **************************************************** + * # *************************************** + * # *************************** + * # ****************** + * # *********** + * # ******* + * # *** + * # * + * */ static VALUE |