List<string> Simple Group and Count?

c# linq-group
tripbrock picture tripbrock · Mar 14, 2012 · Viewed 33.6k times · Source

I have a very simple List<string> setup which contains lots of single characters per item (IE a foreach would console out to "a" "k" "p" etc)

What I'd like to do is be able to group the items and also count how many of each occurs so I'd get an output similar to:

a - 2
t - 3
y - 3

Any tips on the best way to do this?

I am using .Net 4 if that's any help.

Answer

Jon Skeet picture Jon Skeet · Mar 14, 2012

(Given that each entry is a single character, is there any reason you don't have a List<char> by the way?)

How about:

// To get a Dictionary<string, int>
var counts = list.GroupBy(x => x)
                 .ToDictionary(g => g.Key, g => g.Count());

// To just get a sequence
var counts = list.GroupBy(x => x)
                 .Select(g => new { Text = g.Key, Count = g.Count() });

Note that this is somewhat inefficient in terms of internal representation. You could definitely do it more efficiently "manually", but it would also take more work. Unless your list is large, I would stick to this.

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