Using Linq to return each item only once.

Question

Here's what I'm trying to do. Have a use right a sequence of numbers delimited by spaces. After I save those numbers, I want to return a string of all the numbers only once, even if a number has appeared n number of times in the sequence.

string[] tempNumbers = textValue.Split(' ');

IEnumerable<string> distinctNumbers = tempNumbers.Where(value => value.Distinct());

I'm getting this error:

Error   2   Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<char>' to 'bool' c:\users\sergio\documents\visual studio 2010\Projects\LinqPlayground\LinqPlayground\SetSemanticsExample.cs  67  75  LinqPlayground

Answer 1

The extension method IEnumerable.Distinct is not a predicate function. It operates on an IEnumerable<T> and returns a new IEnumerable<T> where each element appears only once.

To fix your code just do this instead:

IEnumerable<string> distinctNumbers = tempNumbers.Distinct();

---

I want to return a string of all the numbers only once

If you want the result as a single space-separated string then in addition to the above you will also need to call string.Join:

string result = string.Join(" ", distinctNumbers.ToArray());
txtResult.Text = result;

Answer 2

Where(value => value.Distinct()) will take each string from the tempNumbers to evaluate. Besides, the string is a collection of chars. That's why you can apply the Distinct() to the

value.

Moreover the result of Distinct() extension method is and IEnumerable<T>, where T is char here. Hence the whole operation causes the exception.

In order to get distinct numbers , you can use the query

var distinctNumbers = (from elem in tempNumbers
                      select elem).Distinct();

Cheers