CODEWITHSUNDEEP
f#
SuperCell
SuperCell

Reputation: 241

How to multiply two two nth elements of a list in F#

So i am trying to multiply the nth element of one list with the nth element of another list and add them together

 let listMulti xList yList =
 |> [for x in xList do
       for y in yList do
           yield x*y ] // multiplies all the elements on x with y
 |> List.filter(fun x-> List.nth % List.length (xList) =1 ) //gets the elements 1 , 4, 7 for a list of size 3. This is scalable
 |> List.sum //add them all up

So the idea here is 

>listMulti [1;2;3][4;5;6];;
val it : int = 32

So 1*4 + 2 *5 + 3*6 = 32 ,but instead im getting

error FS0010: Unexpected infix operator in binding

Help?

Upvotes: 2

Views: 1156

Answers (1)

John Palmer
John Palmer

Reputation: 25516

The error is because you are using List.nth in a weird way.

I would do something like

List.zip xlist ylist
|> List.sumBy (fun (a,b) -> a*b)

Here list.zip combines the lists - so if you had [1;2;3] and [4;5;6] you get [(1,4);(2,5);(3,6)]. Then you just multiply and sum in one go.

Upvotes: 3

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