Recursive function to split list into list

Question

I'm trying to solve the following problem, I have a Collection that contain some data:

+-------------+---------------+-------------+
|     Date    |  InitialValue |  FinalValue |
+-------------+---------------+-------------+
|  21.05.2003 | 0             | 382087.14   |
|  23.06.2003 | 408206.52     | 110622.79   |
|  19.07.2004 | 123811.34     | 0           |
|  31.12.2011 | 0             | 0           |
|  08.06.2012 | 0             | 501854.71   |
|  31.12.2012 | 501854.71     | 546208.19   |
|  31.12.2013 | 634535.58     | 666284.47   |
|  30.06.2014 | 666284.47     | 725837.32   |
|  08.07.2014 | 725837.32     | 729646.48   |
+-------------+---------------+-------------+

What I need to do is to split this list into multiple lists when the final value is equal to 0. The expected result should be something like this:

Result list 1

+-------------+---------------+-------------+
|     Date    |  InitialValue |  FinalValue |
+-------------+---------------+-------------+
|  21.05.2003 | 0             | 382087.14   |
|  23.06.2003 | 408206.52     | 110622.79   |
|  19.07.2004 | 123811.34     | 0           |
+-------------+---------------+-------------+

Result list 2

+-------------+---------------+-------------+
|     Date    |  InitialValue |  FinalValue |
+-------------+---------------+-------------+
|  31.12.2011 |             0 |           0 |
+-------------+---------------+-------------+

Result list 3

+-------------+---------------+-------------+
|     Date    |  InitialValue |  FinalValue |
+-------------+---------------+-------------+
|  08.06.2012 | 0             | 501854.71   |
|  31.12.2012 | 501854.71     | 546208.19   |
|  31.12.2013 | 634535.58     | 666284.47   |
|  30.06.2014 | 666284.47     | 725837.32   |
|  08.07.2014 | 725837.32     | 729646.48   |
+-------------+---------------+-------------+

Can somebody give me an elegant way to solve my problem?

I've tried to use takewhile, but this solve just the first split. I thought about using groupby, but i could not figure out how to group the set of data in the right way — Raphael, Jul 09 '14 at 13:12
This is a near-duplicate of http://stackoverflow.com/q/22847802/1549380. — Zack Butcher, Jul 09 '14 at 13:14
Zack thank you! I have typed the right search, that is what I was looking for! Sorry for the duplicate — Raphael, Jul 09 '14 at 13:18
@Zack Ah, the one line linq solution. Seems to be doing the same as my code but with an aggregate, interesting. Although to be honest, I'd stick with a for loop for easier readability. — Carra, Jul 09 '14 at 13:41
@Carra In production code I probably would as well - that question asked specifically for a LINQ solution, however. It shouldn't be hard to translate that to a loop though, simply replace the Aggregate with `foreach` and declare the required variables (mostly just the `List>`) outside the loop (which is exactly what your answer does). — Zack Butcher, Jul 09 '14 at 13:52

score 4 · Accepted Answer · answered Jul 09 '14 at 13:16

You don't always need linq:

var List<Data> myData;
var List<List<Data>> mySplittedData;

mySplittedData.Add(new List<Data>());
foreach(var item in myData)
{
  mySplittedData.Last().Add(item);
  if(item.FinalValue == 0)
    mySplittedData.Add(new List<Data>());
}

Should work although I'm sure someone will come up with a clever one line linq solution :)

score 1 · Answer 2 · answered Jul 09 '14 at 13:17

I'm not sure if this is elegant, but it uses Linq all the same:

var result = items.Aggregate(new List<List<Item>> { new List<Item>() }, (list, value) =>
{
    list.Last().Add(value);
    if (value.FinalValue == 0)
    {
        list.Add(new List<Item>());
    }
    return list;
});

score 0 · Answer 3 · answered Jul 09 '14 at 13:15

0

Psuedo code

while (more result) {
  list = input.Skip(n).TakeWhile(not 0)
  n += list.Count()
  use or store list
}

Not the most elegant, as the skip will have to skip over the first element of input many times, but might get you started.

answered Jul 09 '14 at 13:15

Jonny

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Recursive function to split list into list

3 Answers3