Slice an Array in half at a given index, but leaving out the index

Question

Given an array

x = [2, 3, 4, 5, 6, 7]

I'd like to slice it in half at a certain point/index and create two subarrays of such cut, but leaving out the index. Example:

x = [2, 3, 4, 6, 70, 10]
left, right = x.slice_at_index(2)
left  = [2, 3]
right = [6, 70, 10]

I've tried with each_index, slice, chunk but can't leave out the index element.

ndnenkov · Answer 1 · 2016-10-18T14:31:52.527

3

left, right = x.take(index), x.drop(index.next)

edited Oct 18 '16 at 14:31

answered Oct 18 '16 at 14:26

ndnenkov

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user3033467 · Answer 2 · 2016-10-18T13:35:20.627

1

left = x[0..1]
right = x[3..-1]

edited Oct 18 '16 at 13:35

answered Oct 18 '16 at 13:33

user3033467

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He is saying " leaving out the index". The value at index should not be present at the result array. – Gopal Oct 18 '16 at 13:34

Oleksandr Holubenko · Answer 3 · 2016-10-18T15:43:48.503

1

I think, docs like about array should help you next time.

So, UPD solution for you:

x = [2, 3, 4, 6, 70, 10]
left, right = x.shift(2), x.drop(2.pred)

> left
=> [2, 3]
> right
=> [6, 70, 10]

edited Oct 18 '16 at 15:43

answered Oct 18 '16 at 14:07

Oleksandr Holubenko

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That's a Good one! – Gopal Oct 18 '16 at 14:09
3

This doesn't leave the element @ index as OP wanted. It also mutates `x`, which is horrific. – ndnenkov Oct 18 '16 at 14:11
Worked like a charm!. Thank you. – Leo Oct 18 '16 at 18:20

score 0 · Answer 4 · answered Oct 18 '16 at 14:14

You can write a method:

def slice_at_index(array, index)
  left = array[0...index]  # 3 dots vs 2
  right = array[(index + 1)..-1]
  return [left, right]
end

But, I would generally avoid multiple assignment such as left, right = slice_at_index(x, 2) as a style rule.

score 0 · Answer 5 · edited May 23 '17 at 12:16

The easiest way, and I think most readable, is to use the range operator .. to specify the indexes you want out of the array.

def slice_at(array, index)
  left = array[0..(index - 1)]
  right = array[(index + 1)..-1]
  return [left, right]
end

If you'd like to learn more about how the range operator works when used this way, read this post.

Remember that you can use ... or .. in Ruby to generate ranges. Using three dots will include the starting point, but exclude the ending point, while using two dots will include both the starting and ending points. See more here.

Slice an Array in half at a given index, but leaving out the index

5 Answers5