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I have a list {1,2,3,4,5,6} which I would like to associate to another list {a,b,c} by the rule {1->a,2->a,3->b,4->b,5->c,6->c}

What is the best way to do this without explicitly writing out the associations?

 Table[Rule[{1, 2, 3, 4, 5, 6}[[i]], {a, b, c}[[Ceiling[i/2]]]], {i, 1, 6}]

works but is it the most efficient way?

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4 Answers 4

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AssociationThread[{1, 2, 3, 4, 5, 6}, Transpose[{{a, b, c}, {a, b, c}}] // Flatten]

(* <|1 -> a, 2 -> a, 3 -> b, 4 -> b, 5 -> c, 6 -> c|> *)
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  • $\begingroup$ Also, AssociationThread[{1, 2, 3, 4, 5, 6}, Table[#, 2] & /@ {a, b, c} // Flatten] $\endgroup$
    – Bob Hanlon
    Jun 17, 2020 at 23:17
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AssociationThread[#, Riffle[#2, #2]] &[Range[6], {a, b, c}]
 <|1 -> a, 2 -> a, 3 -> b, 4 -> b, 5 -> c, 6 -> c|>
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listA = {a,b,c}
listB = Riffle[listA,listA]
MapThread[Rule[#1, #2]&, {Range[6], listB}]
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Here's an approach:

ClearAll[distributeAssociation];
distributeAssociation[list1_, list2_] :=
 With[{n = Length@list2},
  Join @@ MapThread[AssociationThread, {
      Partition[list1, Ceiling[Length@list1/n]],
      list2}] /; Positive[n]];
distributeAssociation[_, {}] = {};

distributeAssociation[{1, 2, 3, 4, 5, 6}, {a, b, c}]
(* <|1 -> a, 2 -> a, 3 -> b, 4 -> b, 5 -> c, 6 -> c|> *)
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