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c#linqparsingint
Alex
Alex

Reputation: 35861

Find all integers in list of strings

Given this list of string values:

"12345", "6789a", "9876", "23467b"

How do we use a Linq statement in C# to select only the integers? In other words, we only want to return 12345 and 9876.

Upvotes: 4

Views: 4511

Answers (4)

Tim Schmelter
Tim Schmelter

Reputation: 460208

One way:

IEnumerable<int> ints = strings.Where(str => str.All(Char.IsDigit))
    .Select(str => int.Parse(str));

This selects only strings where all chars are digits. Then it parses them to int.

A better way is to use this extension:

public static int? TryGetInt(this string item)
{
    int i;
    bool success = int.TryParse(item, out i);
    return success ? (int?)i : (int?)null;
}

Then you can use this query:

IEnumerable<int> ints = strings.Select(str => str.TryGetInt())
    .Where(nullableInt => nullableInt.HasValue)
    .Select(nullableInt => nullableInt.Value);

Upvotes: 6

Roy Dictus
Roy Dictus

Reputation: 33139

The TryParse method of int is the most reliable indicator that you have a proper number.

Use it like this:

int number = 0;
var selected = list.Where(x => int.TryParse(x, out number)).ToList();

Upvotes: 4

Jon
Jon

Reputation: 437504

Filter the list down to only those strings all characters of which are digits:

var filtered = list.Where(s => s.All(char.IsDigit));

An alternative is to use int.TryParse as the filtering function, which has a number of subtle differences in behavior (the rules for what a valid integer is allow more than just digits, see the documentation).

If you want the results typed as integers, follow this up with .Select(int.Parse).

Upvotes: 7

Douglas
Douglas

Reputation: 54897

You can filter your entries based on the return value of the Int32.TryParse method:

int temp;
list.Where(x => int.TryParse(x, out temp));

Upvotes: 14

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