Get certain item from each Tuple from List

Question

What is the correct way to go about creating a list of, say, the first item of each Tuple in a List of Tuples?

If I have a List<Tuple<string,string>>, how would I get a List<string> of the first string in each Tuple?

Answer 1

A little Linq will do the trick:

var myStringList = myTupleList.Select(t=>t.Item1).ToList();

As an explanation, since Tim posted pretty much the same answer, Select() creates a 1:1 "projection"; it takes each input element of the Enumerable, and for each of them it evaluates the lambda expression and returns the result as an element of a new Enumerable having the same number of elements. ToList() will then spin through the Enumerable produced by Select(), and add each element one at a time to a new List<T> instance.

Tim has a good point on the memory-efficiency; ToList() will create a list and add the elements one at a time, which will cause the List to keep resizing its underlying array, doubling it each time to ensure it has the proper capacity. For a big list, that could cause OutOfMemoryExceptions, and it will cause the CLR to allocate more memory than necessary to the List unless the number of elements happens to be a power of 2.

Answer 2

List<string> list = tuples.Select(t => t.Item1).ToList();

or, potentially less memory expensive:

List<string> list = new List<String>(tuples.Count);
list.AddRange(tuples.Select(t => t.Item1));

because it avoids the doubling algorithm of List.Add in ToList.