In Ruby how can I add a nested array to an array without creating an additional layer of nesting?

Question

I'm trying to do something roughly analogous to this

collection = []
pair_one = [[:ae1,:be1],[:ae2,:be2]]
collection << pair_one
pair_two = [[:ae3,:be3],[:ae4,:be4]]
collection << pair_two

The problem is that collection is this:

[[[:ae1, :be1], [:ae2, :be2]], [[:ae3, :be3], [:ae4, :be4]]]

and I want it to be this:

[[:ae1, :be1], [:ae2, :be2], [:ae3, :be3], [:ae4, :be4]]

What method should I use instead of <<?

Basically I want to add the contents of pair_one and pair_two to collection, rather than the arrays themselves. What array method is escaping my memory?

I don't understand the question. Your "I want it to be this" is not a valid Ruby array. The first example is exactly what you should be getting back from your code. — Ryan Bigg
– Ryan Bigg, Commented Nov 7, 2012 at 2:53

iconoclast · Accepted Answer · 2012-11-11 03:24:59Z

2

You can use concat, += or |=

・ concat to avoid unnecessary object creation.
・ |= to eliminate duplicates.

collection = []
#=> []
pair_one = [[:ae1,:be1],[:ae2,:be2]]
collection += pair_one
#=> [[:ae1, :be1], [:ae2, :be2]]
pair_two = [[:ae3,:be3],[:ae4,:be4]]
collection += pair_two
#=> [[:ae1, :be1], [:ae2, :be2], [:ae3, :be3], [:ae4, :be4]]

edited Nov 11, 2012 at 3:24

iconoclast

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answered Nov 7, 2012 at 2:54

Benoît

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7 Comments

Boris Stitnicky Over a year ago

@iconoclast: But +1 to you for asking such a nice question ^_^

x1a4 Over a year ago

There's also Array#concat, which creates fewer objects because it modifies the original array in place.

Niklas B. Over a year ago

@x1a4: I think += is overloaded to do exactly the same thing (modify the original array in place), so there should be no difference performance-wise.

x1a4 Over a year ago

@NiklasB. The docs are saying + returns a new array. If you are aware otherwise, I'd like to find that documentation.

Niklas B. Over a year ago

@x1a4: I was talking about +=, not +. I thought that += is overloaded like in Python, but that doesn't seem to be the case, as a quick test in IRB shows

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