Btukfyl

How do you iterate over the keys or rules of an association (in any order)? E.g. for

<|"0"->0, "1"->1, "2"->2|>

I would like to either iterate over "0", "1", "2".

To iterate over the keys of an association, first get the keys in a list using Keys. then use this in your favorite iteration construct (Do, Table, Scan, Map, etc):

In[16]:= assoc = <|"0" -> 0, "1" -> 1, "2" -> 2|>;



In[17]:= Do[Print[x], {x, Keys[assoc]}]



During evaluation of In[17]:= 0



During evaluation of In[17]:= 1



During evaluation of In[17]:= 2

If you would like to map over the keys to transform them into something else, you can use KeyMap:

a = <|"0" -> 0, "1" -> 1, "2" -> 2|>;

a // KeyMap[("newKey" <> #) &]

(* <|"newKey0" -> 0, "newKey1" -> 1, "newKey2" -> 2|> *)

Otherwise, the good old Map will iterate over the values as if the structure were a list:

a // Map[("newVal" <> ToString@#) &]

(* <|"0" -> "newVal0", "1" -> "newVal1", "2" -> "newVal2"|> *)

You should also look up KeyValueMap to see if that would make your task easier.

Edit

Henrik Schumacher's succinct comment contains everything I have elaborated here. His comment had not been posted when I began writing this answer.