Find minimum by a criteria

Hi, I’m trying to do a function that returns the minimum from a list but it doesn’t let me use the sort function so that I can take the first element after I mapp the list according to the criteria, does anyone has a suggestion of how can I fix it or how can I do this function?
{-| Description for minimumBy

minimumBy .x [ { x = 1, y = 2 } ] --> Just {x = 1, y = 2}

minimumBy .x [] --> Nothing

minimumBy (modBy 10) [ 16, 23, 14, 5 ] --> Just 23

minimumBy : (a → comparable) → List a → Maybe a
minimumBy cond l =
mapped = cond l
sorted = mapped.sort
case l of
→ Nothing
x::xs → Just (sorted.take 1)

Hi @myNameIs I’m not entirely sure of what you are asking. Are looking at how to use the minimumBy function in List.Extra or are you trying to write it yourself?

If you want to write it by first sorting a mapped list, you are on the right track, but your line

sorted = mapped.sort

will not work because there aren’t any methods in Elm, it’s all functions, qualified with their module prefix or not, depending on how you import the module.
In your case, you’d have to write something like:

sorted = List.sort mapped

Same for sorted.take which does not exist. But even then, this would not correspond to the specification you wrote in the description, because you’d be returning the value from the mapped list instead of the original one.
So if you want to do it and return the value from the original list, you could instead use List.sortBy.

minimumBy compareFn list =
   List.head (List.sortBy compareFn list)

This implementation is pretty simple, but quite expensive as you are sorting the full array instead of just looking for its minimum. For now this is probably enough, but when you get more experience with elm, I suggest you look into the implementation in the list-extra package.

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