Shuffle a subset of a list [FINALIZED]

Posted

^{Idea shamelessly stolen from caird and rak1507}

Shuffle a subset of a list of unique, positive integers with uniform randomness, given the indices of that subset. For example, given the list $[A,B,C,D,E,F,G,H]$ and the indices $[0,3,4,5,7]$ (0-indexed), you would extract the list $[A,D,E,F,H]$, shuffle it, and insert the shuffled elements back according to the list of indices. Some possible results of this are (elements that stayed in place are bolded) $$[H,\mathbf{\text{B}},\mathbf{\text{C}},D,A,E,\mathbf{\text{G}},F]$$ $$[A,\mathbf{\text{B}},\mathbf{\text{C}},D,E,F,\mathbf{\text{G}},H]$$ $$[F,\mathbf{\text{B}},\mathbf{\text{C}},E,A,H,\mathbf{\text{G}},D]$$.

Rules

• Every possible rearrangement of the list should have a non-zero chance of being chosen.
• You may use zero- or one-indexing, but please specify which you use.
• The indices in the input are guaranteed to be unique and valid.
• This is [tag:code-golf], so least number of bytes wins.

Test cases

All of these examples use 0-indexing.

List
Indices
Possible output

[1,2,3,4,5,6,7]
[0,1,2,3,4,5,6]
[2,3,6,1,0,4,5], etc.

[1,2,3,4,5,6,7]
[0,2,4,6]
[3,2,7,4,5,6,1], etc.

[93,6,10,1,200,41,78,31,34,27]
[0,3,4,8,9]
[1,6,10,27,93,41,78,31,200,34], etc.

Questions for Meta:

• How do I enforce randomness?
• Is this a dupe?
• Is this uninteresting?

posted almost 4 years ago

CC BY-SA 4.0

2y ago by trichoplax‭

user‭

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