Seq.Fold -> the best way to apply a count down?

Question

I have a Seq like this:

[(1, 0, 10); (5, 1, 10); (5, 0, 10); (8, 1, 10); ...]

And I want to decrease the third element in the tuple by one every time the second element is a 1

[(1, 0, 10); (5, 1, 9); (5, 0, 9); (8, 1, 8); ...]

I was thinking Seq.Fold b/c I need an accumulator but I am not sure how to implement. Am I on the right track?

Answer 1

You just need a map:

[(1, 0, 10); (5, 1, 10); (5, 0, 10); (8, 1, 10); ...] 
|> List.map (function (first,second,third) when second = 1 -> (first,second,third - 1) | other -> other)

Answer 2

I was close, but using the wrong function

Seq.Scan does the trick....