CODEWITHSUNDEEP
rubyarraysiteration
brad
brad

Reputation: 9773

How do I modify an array while I am iterating over it in Ruby?

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.

Upvotes: 96

Views: 78956

Answers (4)

Andrew Park
Andrew Park

Reputation: 7

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.

Upvotes: -1

Mark Byers
Mark Byers

Reputation: 837996

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

Upvotes: 157

Jeff Richardson
Jeff Richardson

Reputation: 51

arr.collect! {|item| item * 3}

Upvotes: 5

Chuck
Chuck

Reputation: 237010

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.

Upvotes: 21

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