how to load a comma separated numbers to List in c#

Question

string formIdList = "8256, 8258, 8362, 8120, 8270, 8271, 8272, 8273, 8257, 8279, 8212, 8213, 8214, 8215, 8216, 8217, 8218, 8219, 8231, 8232, 8233, 8234, 8235, 8242, 8248, 8251, 8252, 8254, 8255, 8262, 8263, 8264, 8265, 8266, 8290, 8292, 8293, 8294, 8300, 8320, 8230, 8227, 8226, 8225, 8224, 8223, 8222, 8221, 8291, 8261, 8241, 8228, 8220, 8211, 8208, 8207, 8206, 8205, 8204, 8203, 8202, 8201, 8153, 8151, 8150, 8130, 8122, 8000, 8101, 8102, 8103";

var temp = formIdList.Split(',');

List<int> ids = new List<int>();

I need to load the temp into ids. I can use a for-loop but I'm sure there is a better way.

Since you know the size of the temp array, initialize your list to that size as to cut back on re-sizing the internal array. And by "better", you mean less code? A For Loop is how it'll be implemented in the end. — Bengie, Jan 10 '12 at 19:27
possible duplicate of [How to create a List from a comma separated string?](http://stackoverflow.com/questions/910119/how-to-create-a-listt-from-a-comma-separated-string) — Igby Largeman, Jan 10 '12 at 19:27
> Simon Fox: var asIntegers = arr.Select(s => int.Parse(s)); http://stackoverflow.com/questions/1297231/convert-string-to-int-in-one-string-of-code-using-linq — Bengie, Jan 10 '12 at 19:30

Darin Dimitrov · Accepted Answer · 2012-01-10T19:25:46.067

24

You could use LINQ:

string formIdList = ...
List<int> ids = formIdList.Split(',').Select(int.Parse).ToList();

edited Jan 10 '12 at 19:25

answered Jan 10 '12 at 19:24

Darin Dimitrov

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+1 - I was just writing an answer that started with "You could use LINQ:" – davisoa Jan 10 '12 at 19:25
+1 - I knew the answer would be using LINQ, but I was waiting for someone to write it :) – Shamim Hafiz - MSFT Jan 10 '12 at 19:26
2

@Anders: It was just fine the way it was, no need to create a new lambda, the `int.Parse()` method fits the delegate just fine. – Jeff Mercado Jan 10 '12 at 19:27
@Anders Abel, please don't update my answer, I don't want to use `.Select(i => int.Parse(i))` as you suggest, I want to use `.Select(int.Parse)` as I initially wrote. – Darin Dimitrov Jan 10 '12 at 19:28
@DarinDimitrov: Sorry, I thought it was a typo, didn't think through it. – Anders Abel Jan 10 '12 at 19:31
@DarinDimitrov, Why do you use `method group`? it's very hard to read and understand. – gdoron Jan 10 '12 at 20:05
@gdoron, code readability is a subjective matter. I prefer my version as it doesn't create an additional anonymous method. – Darin Dimitrov Jan 10 '12 at 20:08
I thought `Group Method` is just a syntax sugar, are you saying that `Method Group` is more efficient? – gdoron Jan 11 '12 at 07:09
@gdoron, what is it that you are calling `Method Group`? Never heard of this notion before. – Darin Dimitrov Jan 11 '12 at 07:12
[Method Group](http://stackoverflow.com/questions/886822/what-is-a-method-group-in-c) see the 2nd answer. – gdoron Jan 11 '12 at 07:58
@gdoron, oh, I didn't know it was called that way. Anyway, as I said, I prefer the shorter version as it avoids the creation of an additional anonymous method. – Darin Dimitrov Jan 11 '12 at 07:59

score 2 · Answer 2 · answered Jan 10 '12 at 19:25

2

List<int> ids = formIdList.Split(',').Select(i=>int.Parse(i)).ToList();

answered Jan 10 '12 at 19:25

ek_ny

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score 1 · Answer 3 · answered Jan 10 '12 at 19:25

1

Maybe you should use something like ids.AddRange(temp), did you try it?

answered Jan 10 '12 at 19:25

Aykut Çevik

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score 1 · Answer 4 · answered Jan 10 '12 at 22:35

Linq is great and all, but you do this with a little less heap-thrashing on your own and have more control over what input you find acceptable. The following will yield the integers from any character enumeration separated by comma's and ignoring all white space.

public static IEnumerable<int> ParseInts(IEnumerable<char> idList)
{
    bool valid = false;
    int working = 0;
    foreach (char c in idList)
    {
        if (c >= '0' && c <= '9')
        {
            valid = true;
            working = (working*10) + (c - '0');
        }
        else if (c == ',')
        {
            if(valid)
                yield return working;
            valid = false;
            working = 0;
        }
        else if(!Char.IsWhiteSpace(c))
        {
            throw new ArgumentOutOfRangeException();
        }
    }
    if (valid)
        yield return working;
}

Then you can fill your collection of ints easily enough by using the List<int> constructor:

string formIdList = "8256, 8258, 8362";
List<int> ids = new List<int>(ParseInts(formIdList));

Just depends on what you intend to do with this, how often, and how large the input will be. For small arrays parsed infrequently I would use the Linq method you already accepted. For higher volumes you might try this instead.

how to load a comma separated numbers to List in c#

4 Answers4