Random subset generator Randomly choose one out of k-length, ordered subset of characters in a string, while only storing a limited number of characters. The subset must be chosen with equal probability and may contain repeated characters. Do this without generating all possible permutations and assume k is at most the length of the string. For example, the string daddy has 7 subsets of length two: da, dd, dy, ad, ay, yd, ya. The function should return any one of them with the probability of 1/7.
Pyth - 5 bytes
While we're arguing about the nomenclature, I'm just guessing at the rules based on the example to just mean pick one from all unique permutations of length n of the string.
O{.PF

Try it online here.