Ruby: How to concatenate array of arrays into one

Question

I have an array of arrays in Ruby on Rails (3.1) where all the internal arrays are of different size. Is there a way to easily concatenate all the internal arrays to get one big one dimesional array with all the items?

I know you can use the Array::concat function to concatenate two arrays, and I could do a loop to concatenate them sequentially like so:

concatenated = Array.new
array_of_arrays.each do |array|
    concatenated.concat(array)
end

but I wanted to know if there was like a Ruby one-liner which would do it in a cleaner manner.

Thanks for your help.

Answer 1

You're looking for #flatten:

concatenated = array_of_arrays.flatten

By default, this will flatten the lists recursively. #flatten accepts an optional argument to limit the recursion depth – the documentation lists examples to illustrate the difference.

Answer 2

Or more generally:

array_of_arrays.reduce(:concat)

Answer 3

You can use flatten! method. eg. a = [ 1, 2, [3, [4, 5] ] ] a.flatten! #=> [1, 2, 3, 4, 5]