# Iterate over keys of association

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

<|"0"->"a", "1"->"b", "2"->"c"|>


I would like to either iterate over "0", "1", "2" or tuples containing each key and value.

For example, something that performed the equivalent of a python dictionary's items, method would be ideal (which returns a list (or iterator) in the form [(key1, value1), ...], so {{"0", "a"}, {"1", "b"}, {"2", "c"}} here).

• Simply use Map, KeyValueMap or KeyMap? Dec 5 '18 at 19:20
• Can you tell what exactly do you want to do?
– Kuba
Dec 5 '18 at 21:42
• Woooops! Done! :) Dec 6 '18 at 7:40
• @SLesslyTall You see, you want KeyValueMap[List] @ asso but who could've known :)
– Kuba
Dec 6 '18 at 7:53

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.