Iterate over a list of maps and sum the result

Questions / Help
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1

I have this list of maps:

list = [%{price: 2, quantity:4}, %{price: 3, quantity: 5}]

For each map on the list, I need to multiply the price by the quantity and then sum all of the results.

In this case it would be: (2 * 4) + (3 * 5) = 23

I’ve tried many ways but I don’t know how to achieve this. I can’t show what I’ve done before because all of that leads nowhere.

I’d appreciate if anyone knows how to do this. Thanks

2 
Enum.reduce(list, 0, fn %{price: price, quantity: quantity}, acc ->
   acc + price * quantity
 end)
2 Likes
3

@Laetitia’s solution is a good one, and it does it in a single pass.

However you could also conceptually split the problem up which might be easier to understand:

list
|> Enum.map(fn %{price: price, quantity: quantity} -> price * quantity end)
|> Enum.sum

This is almost verbatim your problem statement:

For each map on the list, I need to multiply the price by the quantity and then sum all of the results.

The Enum.map multiplies the price by the quantity, and then Enum.sum adds it all up.

1 Like
4

Both solutions are great. Both do the job in a very elegant way. Thanks both for your precious time. I tried both solutions and those are great. I’ll implement yours because it’s easier to read, at least for me

5

Wasn’t there a plan for an official Elixir API like Enum.product btw?

6

https://hexdocs.pm/elixir/master/Enum.html#product/1
as well as
https://hexdocs.pm/elixir/master/Tuple.html#product/1

2 Likes
7

Thanks.

But hmmm, that doesn’t seem exactly as what OP needs then.

8

It’s generally helpful to post it anyways, because folks will be able to help troubleshoot your thinking and make future problems easier.

2 Likes
9

Ok , next time then. Thanks