How to get an array index in LINQ

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I get two strings as input from two separate sources (over which I have no control). The first string strInput will contain one 'X', the position of which should be equal to the value of an element in the pattern string. I need the index of the element in pattern.

I've got it working in regular code using 'for' loops but would like to use LINQ and/or lambdas to make it more succinct. The following returns the value 4, but what I need is the index, which in this case is '1'.

C#

string strInput = "    X       ";           // String from form (this is 4 spaces followed by X followed by n spaces
string pattern = "0,4,6,8,11";              // String containing matching positions of X in string

string place = strInput.IndexOf("X").ToString();        // Get position of X
string[] positions = pattern.Split(',');

var thisIndex = from pos in positions
                where (pos == place)
                select pos.First();

foreach (var x in thisIndex)
{
    Console.WriteLine("This is the index of X: {0}", x);
    Console.ReadLine();
}

Any help would be appreciated.

Posted 3-Apr-11 8:15am

AnnieMacD

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Jonathan Cardy · Accepted Answer · 2011-04-03T08:48:00

Hi Annie!

Try this.

C#

string strInput = "    X       "; // String from form (this is 4 spaces followed by X followed by n spaces
string pattern = "0,4,6,8,11"; // String containing matching positions of X in string

string place = strInput.IndexOf("X").ToString();        // Get position of X (4)
string[] positions = pattern.Split(",");

//Create a temporary structure saving the positions along with their positions.
var result = positions.Select((s, i) => new { Pos = i, Str = s }) 
            .Where(o => o.Str == place) //Pick the item with a position matching the input
            .FirstOrDefault();

if (result != null)
{
    var output = result.Pos;
}

EDIT: This solution is much more succinct, but note that it requires the input to always be valid, so you might want to do some initial checking.

C#

string strInput = "    X       ";           // String from form (this is 4 spaces followed by X followed by n spaces
string pattern = "0,4,6,8,11";              // String containing matching positions of X in string

int place = strInput.IndexOf("X");        // Get position of X (4)
var positions = pattern.Split(",").Select(s => int.Parse(s));

int result = positions.TakeWhile((p, i) => p != place)
                      .Count();