thojanssens1
Sort by multiple values?
Is there an easy way to sort a list of maps by some key, but if those keys are equal, be able to specify another key (and again if equal, another key, and so on)?
E.g.
fruits =
[
%{
color: "yellow",
name: "potato"
},
%{
color: "red",
name: "raspberry"
},
%{
color: "red",
name: "radish"
},
%{
color: "yellow",
name: "pineapple"
},
]
First sort the maps by color ascending, but if equal, by name ascending.
Marked As Solved
hauleth
I cannot find docs to back it up, but I believe that you want Enum.sort_by(list, &{&1.color, &1.name}).
Also Liked
LostKobrakai
Tuples are ordered by size, two tuples with the same size are compared element by element.
https://erlang.org/doc/reference_manual/expressions.html#term-comparisons
sodapopcan
You negate the terms:
Enum.sort_by(list, &{!&1.color, !&1.name})
lud
No, this will sort that list: [{false, false},{false, false},{false, false},{false, false}].
You can just reverse the list. If you want to sort by ascending name but descending color you will have to compute a score or something like that, like mapping colors to integers and multiply them by -1 to get descending order.
al2o3cr
sort_by is stable if EVERYTHING returns the same value:
iex(1)> [%{color: "yellow", name: "potato"}, %{color: "red", name: "apple"}] |> Enum.reverse() |> Enum.sort_by(&{!&1.color, !&1.name})
[%{color: "red", name: "apple"}, %{color: "yellow", name: "potato"}]
This should have returned the map with “yellow” first (like in your second example) if it was meaningfully sorting.
LostKobrakai
At that point I think it makes sense to use a custom compare function, instead of trying to come up with some intermediary, which happens to be sorted correctly without one.
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