Duplicate array elements in Ruby

Question

I have an array rangers = ["red", "blue", "yellow", "pink", "black"] (it's debatable that green should part of it, but I decided to omitted it)

I want to double the array elements so it returns rangers = ["red", "red", "blue", "blue", "yellow", "yellow", "pink", "pink", "black", "black"] in that order.

I tried look around SO, but I could not find find a way to do it in that order. (rangers *= 2 won't work).

I have also tried rangers.map{|ar| ar * 2} #=> ["redred", "blueblue",...]

I tried rangers << rangers #=> ["red", "blue", "yellow", "pink", "black", [...]]

How can I duplicate elements to return the duplicate element value right next to it? Also, if possible, I would like to duplicate it n times, so when n = 3, it returns ["red", "red", "red", "blue", "blue", "blue", ...]

The green ranger is the best one, though. ;P

Julian Kniephoff
– Julian Kniephoff

2016-07-25 18:34:42 +00:00
Commented Jul 25, 2016 at 18:34 — Julian Kniephoff
– Julian Kniephoff, Commented Jul 25, 2016 at 18:34

Julian Kniephoff · Accepted Answer · 2016-07-25 19:34:31Z

9

How about

rangers.zip(rangers).flatten

using Array#zip and Array#flatten?

A solution that might generalize a bit better for your second request might be:

rangers.flat_map { |ranger| [ranger] * 2 }

using Enumerable#flat_map. Here you can just replace the 2 with any value or variable.

edited Jul 25, 2016 at 19:34

answered Jul 25, 2016 at 18:16

Julian Kniephoff

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6 Comments

Mladen Jablanović Over a year ago

also: ([rangers]*n).inject(&:zip).flatten :)

Julian Kniephoff Over a year ago

Oh, very nice @MladenJablanović. ;)

Iggy Over a year ago

Very convenient! I didn't think of using zip + flatten combo. Will prove very handy in the future. Thanks all!

Julian Kniephoff Over a year ago

@MladenJablanović even better in my opinion though: ([rangers] * n).transpose.flatten. This question really inspires me. x)

Cary Swoveland Over a year ago

This card allows you to go directly to flat_map without passing map (I.e. no reason to mention map).

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