Given a list, find Association from index to value

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Asked 6 years, 10 months ago

Modified 6 years, 10 months ago

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I have a list

list = {"a","b","c",…}

and I want the association

<| 1 -> "a", 2 -> "b", 3 -> "c", … |>

This seems like the sort of thing there would be a built-in function for, but I haven't been able to find one.

I could do this using

list // AssociationThread[Range @ Length[#], #] &

Association@MapIndexed[First[#2] -> #1 &, list]

AssociationMap[list[[#]]&, Range @ Length[list]]

but these are all rather unwieldy. Is there a better way?

asked Jan 11, 2017 at 11:33

Stephen Powell

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3

$\begingroup$ I don't think that there is a better way. These seem quite simple to me. AssociationThread[Range@Length[list] -> list] is likely the fastest. $\endgroup$
– Szabolcs
Jan 11, 2017 at 11:34
$\begingroup$ I keep a shorthand for Range@*Length because I use it so often; that would at least shorten your code. $\endgroup$
– Mr.Wizard
Jan 11, 2017 at 12:02
$\begingroup$ @Mr.Wizard - In this case, Range@Length@list is one character shorter than Range@*Length@list $\endgroup$
– Bob Hanlon
Jan 11, 2017 at 13:55
$\begingroup$ @Stephan Powell For nested lists you could do l = {"a", {"b", "c"}}; a = <||>; MapIndexed[AssociateTo[a, #2 -> #1] &, l, {-1}]; $\endgroup$
– M.R.
Jan 11, 2017 at 16:29

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