Get index of lines that match my linq

Question

I have a linq statement and I would like to know if it is possible to get indicies of lines that match my statement? Here it is:

var result = list3.Where(middle => list4.Any(x => x == middle.Middle.category1)).Select(obj => new { obj, dt = DateTime.ParseExact(obj.LeftColumn, dateFormat, CultureInfo.InvariantCulture) })
           .Where(x => x.dt >= datetimepickerChoice1 && x.dt <= datetimepickerChoice2)
           .Select(x => x.obj).ToList();

possible duplicate of [how to find the index particular items in the list using linq?](http://stackoverflow.com/questions/4374237/how-to-find-the-index-particular-items-in-the-list-using-linq) — Lasse Espeholt, Sep 04 '13 at 08:50
At first, you should refactor and beautify your statement, because it is understandable for machine but not for programmer who's doing review of your code. — sgnsajgon, Sep 04 '13 at 08:50
Do you want the index of the matching lines or the original index of the lines that match? — Tim Schmelter, Sep 04 '13 at 08:58

score 4 · Accepted Answer · answered Sep 04 '13 at 08:50

4

You can use the overload of Select (or Where) which projects also the index of the element:

var result = list3.Select((middle, index) => new{ middle, index })
    .Where(x => list4.Any(xx => xx == x.middle.Middle.category1))
    .Select(x => new { x.middle, x.index, dt = DateTime.ParseExact(x.middle.LeftColumn, dateFormat, CultureInfo.InvariantCulture) })
    .Where(x => x.dt >= czas11 && x.dt <= czas22)
    .Select(x => x.index)
    .ToList();

Side-note: consider to change your variable names to be more meaningful. That is unreadable.

answered Sep 04 '13 at 08:50

Tim Schmelter

450,073
74
686
939

Great, exactly what I wanted!! Thank you :) – Michal_LFC Sep 04 '13 at 08:53
@user2592968: Have a look at Tim.Tang's answer. Maybe that is what you want, the index of the matching line instead of the original index of the matching line. – Tim Schmelter Sep 04 '13 at 09:04
Sorry, my mistake. No I see that your answer is correct. Thank you once again! – Michal_LFC Sep 04 '13 at 09:09

score 1 · Answer 2 · answered Sep 04 '13 at 08:51

1

do you mean this?

var result = list3.Where(middle => list4.Any(x => x == middle.Middle.category1))
           .Select(obj => new { obj, dt = DateTime.ParseExact(obj.LeftColumn, dateFormat, CultureInfo.InvariantCulture) })
           .Where(x => x.dt >= czas11 && x.dt <= czas22)
           .Select((x,index) =>new{ x.obj,Index=index}).ToList();

answered Sep 04 '13 at 08:51

Tim.Tang

3,158
1
15
18

This returns the index of the matching lines, so if 3 lines out of 100 match the indices start from 0 and end with 2. I doubt that this is what OP wants. I assume(I may be wrong) that he needs the original index. – Tim Schmelter Sep 04 '13 at 08:56

score 0 · Answer 3 · answered Sep 04 '13 at 09:08

Also note that if you want to search for the indicies of items matching a predicate very often, it could be worth writing a very simple extension method:

public static class IEnumerableExt
{
    public static IEnumerable<int> FindIndices<T>(this IEnumerable<T> self, Predicate<T> predicate)
    {
        int i = 0;

        foreach (var element in self)
        {
            if (predicate(element))
                yield return i;

            ++i;
        }
    }
}

Which you would call like this:

var result = list3.FindIndices(x => list4.Any(xx => xx == x.middle.Middle.category1));

Get index of lines that match my linq

3 Answers3

Linked

Related