Question

Ruby has a select method that takes an array and returns a subarray consisting of all the elements that pass the test given in a block:

myarray.select{|e| mytest(e)}   #=> subarray of elements passing mytest

I am wondering whether there is a simple method to get not these elements, but their indices. I understand you could do this:

indices = []
myarray.each_with_index{|e,i| indices << i if mytest(e)}

But I’m looking for a one-liner. Does one exist? Please don’t write an extension to the Array class, I know you can get a one-liner that way.

Answer 1

Another one-liner:

(0...myarray.length).select {|i| mytest(myarray[i])}

Cheers!