Using scala to accumulate elementwise sums

Question

Possible Duplicate:
In Scala, how do I fold a List and return the intermediate results?

I am searching for a functional way of accumulating the elements of a SortedTree in the following way:

I want a list with containing the sums of all precursors (including the element itself) for all elements in the SortedTree.

For Exmaple:

SortedTree contains (0.4, 0.3, 0.2, 0.1, 0.05)

I want the list: (0,4. 0.7, 0. 9, 1, 1.05)

Any suggestions?

@Tomasz thank you. didn't found that. – peri4n Sep 06 '11 at 08:44 — peri4n, Sep 06 '11 at 08:44

Alexey Romanov · Accepted Answer · 2011-09-06T08:43:15.173

9

There is no SortedTree in the standard library, but you just want scanLeft (assuming your type extends TraversableLike):

seq.scanLeft(0.0)(_ + _).tail

or if you want a list:

seq.toList.scanLeft(0.0)(_ + _).tail

edited Sep 06 '11 at 08:43

answered Sep 06 '11 at 08:36

Alexey Romanov

More like scanLeft than reduceLeft, as the intermediate sums are required – Didier Dupont Sep 06 '11 at 08:43
Yes, already fixed. For some reason I thought for a moment `reduceLeft` worked like `scanLeft` starting with first element instead of `foldLeft` starting with first element. – Alexey Romanov Sep 06 '11 at 08:47
2

Sounds like a good addition to the library, maybe call it `seduceLeft`? – Luigi Plinge Sep 06 '11 at 10:33

1 Answers1