R: generate all permutations of vector without duplicated elements

Question

Is there a straightforward way to generate all possible permutations of a vector of integers (1 to max 999) that specifically excludes duplicated elements?

For example, for a vector with three elements in a range of 1 to 9 the sequence 1 2 3 would be acceptable, as would 1 2 9 but 1 2 2 would be invalid. The sequence must contain exactly n elements (in this case, three). EDIT: to avoid confusion, the order is significant, so 1 2 9 and 9 2 1 are both valid and required.

There are many questions on permutations and combinations using R on SO (such as this and this) but none that seem to fit this particular case. I'm hoping there's an obscure base R or package function out there that will take care of it without me having to write a graceless function myself.

Answer 1

Using gtools package:

require(gtools)
permutations(n = 9, r = 3, v = 1:9)
# n -> size of source vector
# r -> size of target vector
# v -> source vector, defaults to 1:n
# repeats.allowed = FALSE (default)

Answer 2

utils::combn ; combinat::combn or combinat::permn are alternatives.

Answer 3

EDIT: This is not what the OP asked for, but I leave this answer, to avoid confusion.

My math is a little bit rusty, but i think you are describing combinations, not permutations. The base functioncombn() returns combinations.

I illustrate with a manageable set - all combinations of length 3, from the vector 1:4:

combn(4, 3)
     [,1] [,2] [,3] [,4]
[1,]    1    1    1    2
[2,]    2    2    3    3
[3,]    3    4    4    4

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The difference between combinations and permutations is that in combinations the order doesn't matter. So, (2, 3, 4) and (4, 3, 2) is the same combination, but different permutations.