From: Bruce Woodward <bruce.woodward@...>
Date: 2006-04-13T09:30:20+09:00
Subject: map_if, collect_if ???

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Hi,

I have been through the pickaxe book, looking at the array and enumerable
built-in class and module and can't find a way of achieving a map_if or
collect_if.
From pickaxe, collect "Returns a new array containing the results of runnin=
g
block once for every element in enum". Of course map is an alias to collect=
.
There is find_all but it returns an array containing the elements of enum,
not the results of running the block, so I have written one.
Is there a better way that already exists?
thanks,
Bruce.

module Enumerable

  # returns an array containing the results of running block once for every
element in enum, for which block
  # is not false.
  def map_if
    rt, r =3D [], nil
    self.each { |e| (r =3D yield(e)) and rt << r }
    rt
  end
  alias :collect_if :map_if

end

a =3D [ 1,2,3,4,5 ]

b =3D a.map_if { |i|
  (i % 2 !=3D 0) and (i * 10)
}

p b ##  [10, 30, 50]

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