I have this string array:
string[] stringArray = { "fg v1", "ws v2", "sw v3", "sfd v2" };
string value = "v2";
How to get back all indexes of all occurrences value in the array?
so for this example we should get an array of int = [1,3]
preferable without looping.
You can use the LINQ Where extension method to filter, and Select to get the index:
int[] indexesMatched = stringArray.Select((value, index) => new { Value = value, Index = index }
.Where(x => x.Value.Contains("v2"))
.Select(x => x.Index)
.ToArray();
.Select() method had an overload which supported index in the selector too: Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, TResult> selector)That's right. There is no method in the Array-class or extension method in the Enumerable-class which returns all indexes for a given predicate. So here is one:
public static IEnumerable<int> FindIndexes<T>(this IEnumerable<T> items, Func<T, bool> predicate)
{
int index = 0;
foreach (T item in items)
{
if (predicate(item))
{
yield return index;
}
index++;
}
}
Here is your sample:
string[] stringArray = { "fg v1", "ws v2", "sw v3", "sfd v2" };
string value = "v2";
int[] allIndexes = stringArray.FindIndexes(s => s.Contains(value)).ToArray();
It uses deferred execution, so you don't need to consume all indexes if you don't want.
Linq approach
string[] stringArray = { "fg v1", "ws v2", "sw v3", "sfd v2" };
string value = "v2";
int[] result = stringArray.Select((x, i) => x.Contains(value) ? i : -1)
.Where(x => x != -1)
.ToArray();
Same result with Select followed by Where:
var indexes = stringArray.Select((x,i) => x.Contains(searchStr)? i.ToString() : "")
.Where(x=> x!="" ).ToList();
