How do I modify an array while I am iterating over it in Ruby?
RubyArraysIterationRuby Problem Overview
I'm just learning Ruby so apologies if this is too newbie for around here, but I can't work this out from the pickaxe book (probably just not reading carefully enough). Anyway, if I have an array like so:
arr = [1,2,3,4,5]
...and I want to, say, multiply each value in the array by 3, I have worked out that doing the following:
arr.each {|item| item *= 3}
...will not get me what I want (and I understand why, I'm not modifying the array itself).
What I don't get is how to modify the original array from inside the code block after the iterator. I'm sure this is very easy.
Ruby Solutions
Solution 1 - Ruby
Use map to create a new array from the old one:
arr2 = arr.map {|item| item * 3}
Use map! to modify the array in place:
arr.map! {|item| item * 3}
See it working online: ideone
Solution 2 - Ruby
To directly modify the array, use arr.map! {|item| item*3}. To create a new array based on the original (which is often preferable), use arr.map {|item| item*3}. In fact, I always think twice before using each, because usually there's a higher-order function like map, select or inject that does what I want.
Solution 3 - Ruby
arr.collect! {|item| item * 3}
Solution 4 - Ruby
Others have already mentioned that array.map is the more elegant solution here, but you can simply add a "!" to the end of array.each and you can still modify the array. Adding "!" to the end of #map, #each, #collect, etc. will modify the existing array.