get indexes of different elements from arrays with equal length using Linq

Question

I have two arrays with same length. for example

arr1 {1,2,3,4,5,6,7,8,9,0}.
arr2 {1,2,5,3,4,6,7,1,1,0}.

I need to get indexes of elements which are different:

{2,3,4,7,8}

How to do this using Linq?

Maybe this can help you: http://stackoverflow.com/questions/1022986/compare-two-arrays-of-different-lengths-and-show-differences — Juan Ruiz de Castilla, Apr 26 '15 at 08:17

score 4 · Accepted Answer · answered Apr 26 '15 at 08:20

4

The simplest I could think of:

int[] diff = Enumerable.Range(0, arr1.Length).Where(i => arr1[i] != arr2[i]).ToArray();

answered Apr 26 '15 at 08:20

Dennis_E

8,751
23
29

@YuvalItzchakov - this outputs the indices generated by `Enumerable.Range`. – dbc Apr 26 '15 at 08:39

Yuval Itzchakov · Answer 2 · 2015-04-26T08:54:10.647

2

This should work:

int[] arr1 = new[] {1,2,3,4,5,6,7,8,9,0};
int[] arr2 = new[] {1,2,5,3,4,6,7,1,1,0};

var differentIndexes = arr2.Select((item, index) => new { item, index })
                           .Where(x => x.item != arr1[x.index])
                           .Select(x => x.index)
                           .ToArray();

edited Apr 26 '15 at 08:54

answered Apr 26 '15 at 08:29

Yuval Itzchakov

146,575
32
257
321

1

If I swap `arr1` and `arr2`, this outputs `[2,3,4,0,0]` because the `1` appears multiple times. – dbc Apr 26 '15 at 08:41
@dbc You're right. Edited the code (which is a bit uglier now) to actually work for both cases. – Yuval Itzchakov Apr 26 '15 at 08:54

dbc · Answer 3 · 2015-04-27T07:38:17.330

You could use Enumerable.Zip() to walk the arrays in parallel, compare the values, then output matching sequence indices:

        int [] arr1 = new int [] {1,2,3,4,5,6,7,8,9,0};
        int [] arr2 = new int [] {1,2,5,3,4,6,7,1,1,0};

        var query = arr1.Zip(arr2, (i, j) => i != j).Select((b, i) => b ? (int?)i : null).Where(iptr => iptr.HasValue).Select(iptr => (int)iptr);
        Debug.WriteLine(JsonConvert.SerializeObject(query.ToList())); // outputs [2,3,4,7,8]

This doesn't require the sequences to be arrays.

get indexes of different elements from arrays with equal length using Linq

3 Answers3