Print out only odd elements from an IEnumerable?

Question

I am having problems with an array where I for example want to printout the odd numbers in the list.

int[] numbers = new int[]{ 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
Console.WriteLine(numbers.Where(n => n % 2 == 1).ToArray());

The ToString method does not seem to work? I do not want to loop through the elements. What can I do?

Related: https://stackoverflow.com/questions/7481964/how-to-convert-ienumerablestring-to-one-comma-separated-string — StayOnTarget, Mar 19 '21 at 13:53

score 22 · Accepted Answer · answered Feb 22 '11 at 15:09

You need to call String.Join to create a string with the contents of the sequence.

For example:

Console.WriteLine(String.Join(", ", numbers.Where(n => n % 2 == 1));

This uses the new overload which takes an IEnumerable<T>.
In .Net 3.5, you'll need to use the older version, which only takes a string[]:

Console.WriteLine(String.Join(
    ", ", 
    numbers.Where(n => n % 2 == 1)
           .Select(n => n.ToString())
           .ToArray()
    )
);

score 6 · Answer 2 · answered Feb 22 '11 at 15:16

6

In addition to the other answers which point out that you can't just print out an array, I note that this doesn't print out all the odd numbers in the list because your test for oddness is incorrect. Do you see why?

Hint: try testing it with negative numbers. Did you get the expected result? Why not?

answered Feb 22 '11 at 15:16

Eric Lippert

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1

because 5 % 2 is 1 and -5 % 2 is -1 ? – Lukasz Madon Feb 22 '11 at 15:31
5

@lukas: You got it. The correct test for oddness is "x % 2 != 0". – Eric Lippert Feb 22 '11 at 16:20

score 5 · Answer 3 · answered Feb 22 '11 at 15:11

5

You can use ForEach():

 numbers.ToList().ForEach(

    x=> 
  {if(x % 2 == 1)
      Console.WriteLine(x);
  });

answered Feb 22 '11 at 15:11

Aliostad

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Probably no reason to convert it to a List.. Just use foreach (not the extension) off of the enumerable. – Ian P Feb 22 '11 at 15:13
He's refering to `foreach` blocks like `foreach (var x in numbers) { ... }` – Czipperz Jun 26 '19 at 16:22

Print out only odd elements from an IEnumerable?

3 Answers3

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