Maps at scale in Erlang

maps:fold, filter, and merge work the whole table at once.

%% maps:fold, filter, and merge work the whole table at once.
main(_) ->
    Minutes = #{"5560199" => 12, "5560142" => 3, "5560170" => 21},

    Total = maps:fold(fun(_, M, Acc) -> Acc + M end, 0, Minutes),
    io:format("Billed minutes: ~p~n", [Total]),

    Long = maps:filter(fun(_, M) -> M > 10 end, Minutes),
    io:format("Long calls: ~p~n", [maps:size(Long)]),

    Evening = #{"5560142" => 6, "5560188" => 9},
    Merged = maps:merge(Minutes, Evening),
    io:format("All lines: ~p~n", [maps:size(Merged)]),
    io:format("5560142 now: ~p~n", [maps:get("5560142", Merged)]).

How it works

1. maps:fold threads an accumulator over every pair.
2. maps:filter keeps entries its fun approves.
3. merge favors the second map on key collisions.

Keywords and builtins used here

• end
• filter
• fold
• format
• fun
• get
• main
• merge
• size

The run, in numbers

Lines

14

Characters to type

546

Tokens

188

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 188 seconds.

Type this snippet

Step 4 of 4 in Data shapes, step 18 of 31 in Language basics.

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