Merge nested array and regular array by first element

Question

I am trying to merge a regular array array into a nested array such that a given element of a row in the nested array is replaced with each element in the regular array but can't compile the logic into a method e.g:

a1 = [[0,0], [0,0], [0,0]]

a2 = [1,1,1]

=> [[1, 0], [1, 0], [1, 0]] or [[0, 1], [0, 1], [0, 1]]

So far I have:

 a1[0][0, a2[0]] = a2[0]
 a1[1][0, a2[1]] = a2[1]
 a1[2][0, a2[1]] = a2[2]

Which gives the required result but this needs to be wrapped in a method such that any array sizes can be used.

Use zip with map. Or map.with_index on a1 referencing a2 with the block index parameter. — Sagar Pandya
– Sagar Pandya, Commented Nov 28, 2017 at 19:47
You could improve your example by making the elements more varied. For example, a1 = [[0,1], [2,3],[4,5]] and a2 = [6,7,8]. Also, it's best to ask for a specific return value for your example, rather than "this or that". If you specify "this", the return value for "that" can often be easily deduced. — Cary Swoveland
– Cary Swoveland, Commented Nov 28, 2017 at 20:57

souslov · Accepted Answer · 2017-11-28 20:18:33Z

2

You can use map (with first or last, depending on which element from a1 you want to fetch) and zip

a1.map(&:first).zip(a2)
# => [[0, 1], [0, 1], [0, 1]]

Demonstration

answered Nov 28, 2017 at 20:18

souslov

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2 Comments

Cary Swoveland Over a year ago

Consider putting that in the form of a method def m(a1,a2,a1_index)....

safikabis Over a year ago

@CarySwoveland thanks, that was exactly what I needed

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