Get all (n-choose-k) combinations of length n

How can I get all combinations (in order) of length n from a list of numbers? For example, given the list [1, 2, 3, 4], and setting n = 3, how can I get these results?

[1, 2, 3][1, 2, 4][1, 3, 4][2, 3, 4]

_{For combinations of all possible lengths, see Get all possible (2^N) combinations of a list’s elements, of any length . Note that this is not simply a matter of iterating over the possible lengths and combining the results, as there are other reasonable approaches to the problem.}

_{To avoid duplicate outputs when the input has duplicate elements, see Python combinations without repetitions .}

_{Also related: Generate all binary strings of length n with k bits set}