galbangi
Sum of list of maps
hi i am having problem with enum reduce. i am trying to sum values from lat of maps. getting error can any body help please
list = [
%{“price” => “100”, “trans_type” => “cr”},
%{“price” => “100”, “trans_type” => “db”},
%{“price” => “300”, “trans_type” => “cr”}
]
Enum.reduce(list, fn item, acc → %{val: String.to_integer(item[“price”]) + String.to_integer(acc[“price”])} end)
** (ArgumentError) errors were found at the given arguments:
1st argument: not a binary
:erlang.binary_to_integer(nil)
(stdlib 3.15.1) erl_eval.erl:685: :erl_eval.do_apply/6
(stdlib 3.15.1) erl_eval.erl:477: :erl_eval.expr/5
(stdlib 3.15.1) erl_eval.erl:791: :erl_eval.eval_map_fields/5
(stdlib 3.15.1) erl_eval.erl:260: :erl_eval.expr/5
(elixir 1.12.2) lib/enum.ex:2385: Enum.“-reduce/2-lists^foldl/2-0-”/3
thanks
Most Liked
APB9785
If the end result you want is an integer, then it’s best to start with an integer as the accumulator, like this:
Enum.reduce(list, 0, fn item, acc ->
acc + String.to_integer(item[”price”])
end)
qhwa
I just want to point out why you received that error.
reduce(list, fn item, acc -> do_something(...) end)
The result of the do_something(...) will be passed as the new acc. It is a map (%{val: 200}) after the first round of run.
String.to_integer(%{val: 200}["price"]}) leads to the exception. So you just need to change :val into "price" as the map key to bypass the exception. But the above approaches provided by @hudsonbay @APB9785 and @mpope are better IMO.
hudsonbay
list
|> Enum.map(fn %{"price" => price} -> price
|> String.to_integer() end)
|> Enum.sum()
Result: 500
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