Find index of an array in List of arrays in C#

Question

If you had a List of arrays like:

List<int[]> ListOfArrays = new List<int[]>();
ListOfArrays.Add(new int[] { 1, 1 });
ListOfArrays.Add(new int[] { 2, 1 });

How would you find the index of { 2, 1} in the List?

I do not want to use an iteration loop. I would like a concise method like the one suggested by PaRiMaL RaJ in Check if string array exists in list of string:

list.Select(ar2 => arr.All(ar2.Contains)).FirstOrDefault();

(the above code will return true if members of a given string array exist in a list of string arrays)

The only way to avoid an iteration loop will be a dictionary respectively a hash-lookup-table. — xXliolauXx
– xXliolauXx, Commented Oct 31, 2015 at 12:19
@xXliolauXx By iteration I think he means LINQ instead of a hand written loop. — Yuval Itzchakov
– Yuval Itzchakov, Commented Oct 31, 2015 at 12:23
@Yuval ah I see... I thought it was the performance he wanted to keep high... And I thought of LinQ using loops too... — xXliolauXx
– xXliolauXx, Commented Oct 31, 2015 at 12:35

Evgeni Dimitrov · Accepted Answer · 2015-10-31 12:23:45Z

9

var myArr = new int[] { 2, 1 };
List<int[]> ListOfArrays = new List<int[]>();
ListOfArrays.Add(new int[] { 1, 1 });
ListOfArrays.Add(new int[] { 4, 1 });
ListOfArrays.Add(new int[] { 1, 1 });
ListOfArrays.Add(new int[] { 2, 1 });

int index = ListOfArrays.FindIndex(l => Enumerable.SequenceEqual(myArr, l));

answered Oct 31, 2015 at 12:23

Evgeni Dimitrov

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2 Comments

Yuval Itzchakov Over a year ago

You can shorten it a bit: ListOfArrays.FindIndex(l => l.SequenceEqual(myArr));

awesoon Over a year ago

ListOfArrays.FindIndex(myArr.SequenceEqual); should also work

Markus Gilli · Accepted Answer · 2015-10-31 12:20:16Z

1

You can use the SequenceEqual method for this. See MSDN: https://msdn.microsoft.com/en-us/library/vstudio/bb348567(v=vs.100).aspx

answered Oct 31, 2015 at 12:20

Markus Gilli

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1 Comment

Saeid Over a year ago

Thanks Markus, I would have to use a foreach loop over the List and check each member. There should be a more clever way.. :/

deeiip · Accepted Answer · 2015-10-31 12:25:58Z

1

You can try this:

List<int[]> ListOfArrays = new List<int[]>();
ListOfArrays.Add(new int[] { 1, 1 });
ListOfArrays.Add(new int[] { 2, 1 });
var chk = ListOfArrays.FindIndex(e => (e.SequenceEqual(new int[] { 2, 1 })));

edited Oct 31, 2015 at 12:25

answered Oct 31, 2015 at 12:24

deeiip

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