LINQ Numerical Grouping

Question

Looking for a way to group in sets of n elements with LINQ.

I.e:

{1,2,3,4,5,6,7,8,9}:

Grouped By 2: {{1,2},{3,4},{5,6},{7,8},{9}}
Grouped By 3: {{1,2,3},{4,5,6},{7,8,9}}
Grouped By 4: {{1,2,3,4},{5,6,7,8},{9}}
Etc...

Only way I can think of doing something like this at the moment is by using an anonymous type to generate a group index, then grouping by that index. I'm looking for a cleaner solution if possible.

Example:

int groupSize = n;
int groupCount = 0;
int groupNum = 0;

IEnumerable<T> items;
IEnumerable<IGrouping<int,T>> groups = items
    .Select(i => new 
    {
      Index = ((groupCount++) % groupSize == 0) ? groupNum++ : groupNum,
      Item = i
    })
    .GroupBy(c => c.Index, d => d.Item);

I'd like to avoid something this nasty if possible.

It would be awesome if there's a better way, but I don't think there is. — Jeff Schumacher, Jun 04 '10 at 20:07
I mean, I could always write the above as an extension function, I just don't know how the delayed execution would work with something like that. I'd prefer things to be as LINQ'y as possible :) — Aren, Jun 04 '10 at 20:10

Yuriy Faktorovich · Accepted Answer · 2010-06-04T20:23:35.990

6

var values = new []{ 1, 2, 3, 4, 5, 6, 7, 8, 9 };

groups = values.Select((v, i) => new { index = i, value = v })
    .GroupBy(k => k.index / n, e => e.value);

edited Jun 04 '10 at 20:23

answered Jun 04 '10 at 20:17

Yuriy Faktorovich

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!!! The Index, I forgot `.Select` could return it! Thankyou! – Aren Jun 04 '10 at 20:22

score 0 · Answer 2 · edited May 23 '17 at 10:24

0

I've answered a similar question here. It still uses an anonymous type, but I don't think it's as "nasty" as your example.

edited May 23 '17 at 10:24

Community

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answered Jun 04 '10 at 20:23

GWB

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LINQ Numerical Grouping

2 Answers2