Conversion of rule to list values

Question

How can I convert the this rule to a list:

input = {1 -> {71.52, 55.33}};

to:

output = {71.52, 55.33}

Answer 1

For versions before 10.0, use Replace

Replace[1, input]
(* {71.52, 55.33} *)

I prefer to avoid ReplaceAll when Replace is appropriate. ReplaceAll works at all levels in an expression and is thus less predictable (or it makes a bigger mess if there's a bug in my code). Consider if you can potentially have multiple non-atomic keys in the rule list, some of which are sub-parts of others, e.g. {1 -> ..., a[1] -> ...}.

For 10.0 or later versions, use Lookup

Lookup[input, 1]
(* {71.52, 55.33} *)

Lookup is better for this use because it tells you if the key is missing from input.

Answer 2

In general, you can convert list of rules into list of values, in the one of following four ways:

Last @@@ input
input[[All, 2]]
input /. Rule -> (#2 &)
Values@input

Answer 3

it could be convenient to use Association for this, depending on what you are actually doing..

  Association[input][1]

{71.52, 55.33}