Ruby equivalent to Python's "array[i:]" to select all array elements after i?

Question

I find myself wanting something like Python's

ary = [1,2,3,4,5,6,7,8]
ary[2:] #=> [3,4,5,6,7,8]

ALL of the time these days.

The solution always ends up being multi-lined and ugly. I'm wondering what the most elegant solutions out there might be, because mine are not worth showing.

The -1 in a Range is somewhat ugly and magic when used in this context ( e.g. (2..-1).each doesn't match this behaviour). — Neil Slater
– Neil Slater, Commented Mar 27, 2014 at 16:35
If you want to keep the first n items, and can alter arr, you can use front = arr.shift(n). A less-desirable alternative to drop(n) is last(arr.size-n). — Cary Swoveland
– Cary Swoveland, Commented Mar 27, 2014 at 16:44
Note that Array#[] is a.k.a Array#slice: ary[2..-1] can be written ary.slice(2..-1). — Cary Swoveland
– Cary Swoveland, Commented Mar 27, 2014 at 18:36

Kirti Thorat · Accepted Answer · 2014-03-27 16:33:58Z

15

Use Array#drop

2.1.0 :019 > ary.drop(2)
 => [3, 4, 5, 6, 7, 8]

answered Mar 27, 2014 at 16:33

Kirti Thorat♦

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2 Comments

Matheus Moreira Over a year ago

This is the best answer. It works with all Enumerables and even lazy enumerators. To perform the opposite operation, there is the take(n) method. Also available are the drop_while and take_while methods.

Arup Rakshit Over a year ago

Indeed.. It is best.. :)

toro2k · Accepted Answer · 2014-03-27 16:45:19Z

11

You can write:

ary[2..-1]
# => [3,4,5,6,7,8]

-1 is the index of the last element in the array, see the doc for Array#[] for more informations.

A better alternative in Ruby is to use the Array#drop method:

ary.drop(2)
# => [3,4,5,6,7,8]

edited Mar 27, 2014 at 16:45

answered Mar 27, 2014 at 16:32

toro2k

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1 Comment

boulder_ruby Over a year ago

I used to use the #drop thing, but -1 symbolizing the last element in an array is ultimately the easiest way to remember how to do this and all sorts of other permutations of this sort of thing

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