How to convert this indexed LINQ Restriction Operation to the other style of LINQ

Question

just got curious if this LINQ Statement:

  string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
  var shortDigits = digits.Where((digit, index) => digit.Length < index);

is convertible to this style of LINQ:

  var shortDigits  = from d in digits
                     ..........

If yes, can you please show me how...

Answer 1

The problem you're having is that the overload of Where that you're using isn't supported in the fluent query syntax.

You can however get around this by performing a select first and projecting the index into your results like so:

var digitsWithIndex = digits.Select((d, i) => new { Digit = d, Index = i });

You can then consume the index in the fluent query syntax:

var query = from d in digitsWithIndex
            where d.Digit.Length < d.Index
            //just select the digit, we don't need the index any more
            select d.Digit;

This yields the results "five", "six", "seven", "eight", "nine".

I think in this situation I'd recommend sticking with using lambda syntax though, but that's my personal preference.

Here's the full code that I knocked up in LinqPad:

var digits = new []
{
    "zero",
    "one",
    "two",
    "three",
    "four",
    "five",
    "six",
    "seven",
    "eight",
    "nine",
};

var digitsWithIndex = digits.Select((d, i) => new { Digit = d, Index = i });

var query = from d in digitsWithIndex
            where d.Digit.Length < d.Index
            //just select the digit, we don't need the index any more
            select d.Digit;