How do I combine array values with array of hashes?

Question

I have an array of hashes:

[{:foo => 1, :bar => 2}, {:foo => 2, :bar => 4} ...]

And an array of integers:

[3, 6]

I want combine the values from the integer array and the hashes to end up with something like:

[{:foo => 1, :bar => 2, :baz => 3}, {:foo => 2, :bar => 4, :baz => 6}]

I am currently doing this:

myArrayOfHashes.each_with_index |myHash, index|
    myHash[:baz] = myArrayOfIntegers[index]
end

Is that the right approach?

I was imagining a more functional approach where I iterate over both arrays simultaneously, like something using zip + map.

It's not necessary to repeatedly specify you want to do this with Ruby. The tags you set will tell us the language and features or libraries. — the Tin Man, Jun 21 '13 at 07:02
Yeah, good call @theTinMan. Just never sure if favorite tags are used by the person who could answer. But, noted for the future. — sberry, Jun 21 '13 at 07:06
If someone tries to answer who *hasn't* paid attention to the tags, the odds are really good they'll get plenty of down-votes for not having paid attention. They won't repeat that. — the Tin Man, Jun 21 '13 at 07:08
Your current implementation looks good enough for me already — John Dvorak, Jun 21 '13 at 07:09

the Tin Man · Accepted Answer · 2013-06-21T07:22:30.687

6

Try:

require 'pp'

ary_of_hashes = [{:foo => 1, :bar => 2}, {:foo => 2, :bar => 4}]
[3, 6].zip(ary_of_hashes).each do |i, h|
  h[:baz] = i
end

pp ary_of_hashes

Which results in:

[{:foo=>1, :bar=>2, :baz=>3}, {:foo=>2, :bar=>4, :baz=>6}]

zip is a good tool for this, but map won't really buy much, at least nothing that you can't do as easily with each in this case.

Also, don't name variables using CamelCase like myArrayOfHashes, instead use snake_case, like ary_of_hashes. We use CamelCase for class names. Technically we can used mixed case for variables, but by convention we don't do that.

And, it's possible to use each_with_index, but it results in awkward code, because it forces you to use an index into [3, 6]. Let zip join the respective elements of both arrays and you'll have everything you need to massage the hash.

edited Jun 21 '13 at 07:22

answered Jun 21 '13 at 07:07

the Tin Man

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Try `ri Kernel.pp` from the command-line, or check http://www.ruby-doc.org/stdlib-2.0/libdoc/pp/rdoc/index.html – the Tin Man Jun 21 '13 at 07:13
Very good. I figured I could use zip here and do exactly this, not sure what mistake I was making when I tried it earlier. – sberry Jun 21 '13 at 07:20
Yeah, I also follow those conventions when actually writing code. I am not sure why I decided to write my sample like that - I guess too much scala recently. – sberry Jun 21 '13 at 07:23

toro2k · Answer 2 · 2013-06-21T09:02:19.980

6

map is useful when you want to leave the original objects intact:

a = [{:foo => 1, :bar => 2}, {:foo => 2, :bar => 4}]
b = [3,6]
a.zip(b).map { |h, i| h.merge(baz: i) }
# => [{:foo=>1, :bar=>2, :baz=>3}, {:foo=>2, :bar=>4, :baz=>6}]
a.inspect
# => [{:foo=>1, :bar=>2}, {:foo=>2, :bar=>4}]

edited Jun 21 '13 at 09:02

answered Jun 21 '13 at 07:08

toro2k

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According to the code sample in the question, it should be `a.zip(b).each {|h, i| h.update(baz: i)}` rather than creating a new Hash and leaving `a` unchanged. – Arie Xiao Jun 21 '13 at 07:15
I may have been over-reaching with looking to use map since it looks like it might not be necessary. + 1 still though. – sberry Jun 21 '13 at 07:22

score 3 · Answer 3 · answered Jun 21 '13 at 07:24

3

array_of_hashes.each { |hash| hash.update baz: array_of_integers.shift }

answered Jun 21 '13 at 07:24

Boris Stitnicky

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Good (+1) but it destroys `array_of_integers`. – undur_gongor Jun 21 '13 at 07:25
Caution with `array_of_integers.shift`. It'll be destructive. – the Tin Man Jun 21 '13 at 07:26
Right, to preserve the array of integers, `array_of_integers.dup` should be called first. – Boris Stitnicky Jun 21 '13 at 07:27
@BorisStitnicky how is mine? :) – Arup Rakshit Jun 21 '13 at 08:20
@OMG: Mandadory +1 first, now lemme see ... you are running an index ... bad ... but using `with_index` ... good ... ... ... A valid possibility; I'd have used more whitespaces. – Boris Stitnicky Jun 21 '13 at 08:25
@BorisStitnicky I got down-vote. But could you edit my answer as you suggested, I don't understand your advise :(.. – Arup Rakshit Jun 21 '13 at 08:45
1

@OMG: Your option is legitimate, but voting mistakes happen. But if you really want to contribute, don't you happen to know the answer to [this question of mine](http://stackoverflow.com/questions/17203731)? I thought it was just a simple JavaScript question, but it's already up for 2 days, and nothing. – Boris Stitnicky Jun 21 '13 at 08:55

How do I combine array values with array of hashes?

3 Answers3