I have a List<List<Tuple<int, int, int>>>
variable and I want to split it to three List<List<int>>
s. I already can enumerate the list three time like this:
List<List<Tuple<int, int, int>>> tuples = ...
List<List<int>> a = tuples.Select(x => x.Select(y => y.Item1).ToList()).ToList();
List<List<int>> b = tuples.Select(x => x.Select(y => y.Item2).ToList()).ToList();
List<List<int>> c = tuples.Select(x => x.Select(y => y.Item3).ToList()).ToList();
But, can I make all three lists at once using LINQ? Something like:
Tuple<List<List<int>>, List<List<int>>, List<List<int>>> splitted = tuples.Magic(...);
Edit: (This is added after tymtam and Mong Zhu posted their answers)
To be more clear, later when I said "at once", I was concerning performance. I don't really care about actual type of outcome and I don't have obsession with doing it in single line.
Performance-wise Comparison:
This is my code to compare splitting 1000 lists of 1000 tuples, (50 calls, 4000 sample/s):
private void Split_Loop(List<List<Tuple<int, int, int>>> tuples)
{
List<List<int>> a = new List<List<int>>(tuples.Count);
List<List<int>> b = new List<List<int>>(tuples.Count);
List<List<int>> c = new List<List<int>>(tuples.Count);
for (int i = 0; i < tuples.Count; i++)
{
int n = tuples[i].Count;
List<int> l1 = new List<int>(n);
a.Add(l1);
List<int> l2 = new List<int>(n);
b.Add(l2);
List<int> l3 = new List<int>(n);
c.Add(l3);
for (int j = 0; j < n; j++)
{
l1.Add(tuples[i][j].Item1);
l2.Add(tuples[i][j].Item2);
l3.Add(tuples[i][j].Item3);
}
}
}
private void Split_Linq3(List<List<Tuple<int, int, int>>> tuples)
{
List<List<int>> a = tuples.Select(x => x.Select(y => y.Item1).ToList()).ToList();
List<List<int>> b = tuples.Select(x => x.Select(y => y.Item2).ToList()).ToList();
List<List<int>> c = tuples.Select(x => x.Select(y => y.Item3).ToList()).ToList();
}
private void Split_tymtam(List<List<Tuple<int, int, int>>> tuples)
{
IEnumerable<List<List<int>>> a = new Func<Tuple<int, int, int>, int>[]
{ t => t.Item1, t => t.Item2, t => t.Item3 }.
Select(f => tuples.Select(x => x.Select(f).ToList()).ToList());
List<List<List<int>>> b = a.ToList();
}
private void Split_Mong(List<List<Tuple<int, int, int>>> tuples)
{
Func<List<List<Tuple<int, int, int>>>, Func<Tuple<int, int, int>, int>, List<List<int>>> selectorGen = (x, t) => x.Select(y => y.Select(t).ToList()).ToList();
Tuple<List<List<int>>, List<List<int>>, List<List<int>>> splitted = Tuple.Create(
selectorGen(tuples, t => t.Item1),
selectorGen(tuples, t => t.Item2),
selectorGen(tuples, t => t.Item3));
}
private void button3_Click(object sender, EventArgs e)
{
int outer = 1000;
int inner = 1000;
List<List<Tuple<int, int, int>>> tuples = new List<List<Tuple<int, int, int>>>(outer);
for (int i = 0; i < outer; i++)
{
List<Tuple<int, int, int>> list = new List<Tuple<int, int, int>>(inner);
tuples.Add(list);
for (int j = 0; j < inner; j++)
{
Tuple<int, int, int> tuple = new Tuple<int, int, int>(i + j + 1, i + j + 2, i + j + 3);
list.Add(tuple);
}
}
for (int i = 0; i < 50; i++)
{
Split_Loop(tuples);
Split_Linq3(tuples);
Split_tymtam(tuples);
Split_Mong(tuples);
}
}
This is the best I can do:
IEnumerable<List<List<int>>> myLists = new Func<Tuple<int, int, int>, int>[]
{ t => t.Item1, t => t.Item2, t => t.Item3 }
.Select(f => tuples.Select(x => x.Select(f).ToList()).ToList());
You could define a selector function, that takes your tuples
collection and a selector for the tuple item as input and returns a List<List<int>>
:
Func<List<List<Tuple<int, int, int>>>, Func<Tuple<int, int, int>, int>, List<List<int>>> selectorGen = (x,t) => x.Select(y => y.Select(t).ToList()).ToList();
now you can apply this selector to extract the individual items into the corresponding lists while you create a tuple containing the resulting collections:
Tuple<List<List<int>>, List<List<int>>, List<List<int>>> splitted = Tuple.Create(
selectorGen(tuples, t => t.Item1),
selectorGen(tuples, t => t.Item2),
selectorGen(tuples, t => t.Item3));
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