Javascript - range of 5 around index in array

Question

I was wondering how to do the follow.

I have an array of objects and I'm trying to retrieve a set amount eg of them around a given index.

Here's an example.

var arr = [0,1,2,3,4,5,6,7,8,9,10];
var index = 0;
var max = 5;

If the index is 0 I want [0 - 4]
If the index is 4 I want [2 - 6]
If the index is 9 I want [6 - 10]

But I also want it to work if the array is smaller then the max too. Eg

var arr = [0,1,2];
var index = 0;
var max = 5;

Any index would return [0 - 2]

Any thoughts?

The second one should return 0-3 although there's only 0-2 in the array? How should this work? Will it guess? — YMMD
– YMMD, Commented May 13, 2012 at 8:26

Joseph · Accepted Answer · 2012-05-13 08:36:07Z

4

You might want to try this

var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

function getRange(array, index, range) {
    var least = index - Math.floor(range/2);
    least = (least < 0) ? 0 : least;
    return array.slice(least, least+range);
}

answered May 13, 2012 at 8:36

Joseph

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Pavel Strakhov · Accepted Answer · 2012-05-13 08:33:54Z

0

var start = index - max / 2;
if (start < 0) start = 0;
var end = start + max;
if (end > arr.length) {
  end = arr.length;
  start = end - max;
  if (start < 0) start = 0;
}
var result = arr.slice(start, end);

edited May 13, 2012 at 8:33

answered May 13, 2012 at 8:27

Pavel Strakhov

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3 Comments

hooligan Over a year ago

Thanks for the reply, Riateche. I have tried slice. My problem is that I want the index to appear in the middle of the range. So if I have an index of 2 I should get the two results to the left and two to the right where possible. But I always want 5 results where possible too.

Joseph Over a year ago

this only goes forward from the index, not backwards

YMMD Over a year ago

You may also want to check if index + max > arr.length, in order to fulfill this wish: If the index is 9 I want [6 - 10]

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