C# How to find out if array includes string twice

Question

i want to check if a string array includes a string more than one time.

for example

string[] array = new string[]{"A1","A2","A3"};
string item = "A1";

look for item in array, include item just once return false

string[] array = new string[]{"A1","A2","A3","A1"};
string item = "A1";

return true

Any insight would be greatly appreciated.

Or array.Distinct() and comparing this length vs original will check for all entries — Sayse
– Sayse, Commented Jul 28, 2014 at 14:27
@Sayse That will return if any item is repeated, not for the particular item. — Sriram Sakthivel
– Sriram Sakthivel, Commented Jul 28, 2014 at 14:28
@SriramSakthivel - The first sentence is slightly ambiguous which is why I built upon Mohammads comment — Sayse
– Sayse, Commented Jul 28, 2014 at 14:29
@Selman22 I strongly suspect is this a duplicate of the related thread? Find some other question please, or reopen it. — Sriram Sakthivel
– Sriram Sakthivel, Commented Jul 28, 2014 at 14:31

Selman Genç · Accepted Answer · 2014-07-28 14:45:48Z

2

If you want to know whether or not a particular item is repeated more than once, you can get the count of the item and check if it is bigger than 1:

bool isRepeated = array.Count(x => x == item) > 1;

Or, you can do it more efficiently with a HashSet:

bool isRepeated = false;
var set = new HashSet<int>();
foreach(var x in array)
{
    if(x == item && !set.Add(x)) 
    {
       isRepeated = true; 
       break;
    }
}

answered Jul 28, 2014 at 14:45

Selman Genç

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