Concatinating array with subarrays

Question

given this array:

[ ["a", ["example1"]], ["a", ["example2"]], ["b", ["example3"]] ]

would like to merge each array with the same 'beginning'

result should be:

[ ["a", ["example1"], ["example2"]], ["b", ["example3"]] ]

i tried different points from http://www.ruby-doc.org/core-2.2.0/Array.html so far, but i dont get the correct condition to match the elements against each other.

hirolau · Accepted Answer · 2015-01-23 17:15:07Z

2

This can be done using the built in functions group_by,map and flatten

x = [ ["a", ["example1"]], ["a", ["example2"]], ["b", ["example3"]] ]

p x.group_by(&:first).map{|x,y|[x,y.map(&:last)].flatten(1)} #=> ["a", ["example1"], ["example2"], ["b", ["example3"]]

edited Jan 23, 2015 at 17:15

answered Jan 23, 2015 at 11:53

hirolau

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3 Comments

SG 86 Over a year ago

Thanks, +vote for solution without hash type casting

hirolau Over a year ago

Thank, but as a and b seems to be some kind of keys I would, if I could, try to store the data in a hash. But I do not, of course, know the nature of your data so I will no tell you what is best for you.

bluexuemei Over a year ago

more easier code：x.group_by(&:first).map{|x,y|[x,*y.map(&:last)]}

Arup Rakshit · Accepted Answer · 2015-01-23 12:25:23Z

0

I'd do :

array = [ ["a", ["example1"]], ["a", ["example2"]], ["b", ["example3"]] ]

output = array.each_with_object(Hash.new { |h,k| h[k] = [] }) do |in_ary, hash|
  hash[in_ary.first].concat(in_ary[1..-1])
end.map { |k, v| [k, *v] }
output # => [["a", ["example1"], ["example2"]], ["b", ["example3"]]]

edited Jan 23, 2015 at 12:25

answered Jan 23, 2015 at 12:17

Arup Rakshit

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