R help - Nov 2009 - partial cumsum

Hello,

I am searching for a function to calculate "partial" cumsums.

For example it should calculate the cumulative sums until a NA appears,
and restart the cumsum calculation after the NA.

this:

x <- c(1, 2, 3, NA, 5, 6, 7, 8, 9, 10)

should become this:

1 3 6 NA 5  11  18  26  35  45


any ideas?

thank you and best regards,

    stefan

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of smu
> Sent: Wednesday, November 11, 2009 7:58 AM
> To: r-help at r-project.org
> Subject: [R] partial cumsum
> 
> Hello,
> 
> I am searching for a function to calculate "partial" cumsums.
> 
> For example it should calculate the cumulative sums until a 
> NA appears,
> and restart the cumsum calculation after the NA.
> 
> this:
> 
> x <- c(1, 2, 3, NA, 5, 6, 7, 8, 9, 10)
> 
> should become this:
> 
> 1 3 6 NA 5  11  18  26  35  45
Perhaps
   > ave(x, rev(cumsum(rev(is.na(x)))), FUN=cumsum)
    [1]  1  3  6 NA  5 11 18 26 35 45

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 
 
> any ideas?
> 
> thank you and best regards,
> 
>     stefan
> 
> ______________________________________________
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>

quote:
    > x <- c(1, 2, 3, NA, 5, 6, 7, 8, 9, 10)
    > rev(cumsum(rev(is.na(x))))
     [1] 1 1 1 1 0 0 0 0 0 0
A more natural way to do this is
    > cumsum(is.na(c(NA,x[-length(x)])))
     [1] 1 1 1 1 2 2 2 2 2 2
endquote

Both of which suggest the original problem could also be dealt with by 
using rle().  Something like

xna<-is.na(x)
rle(xna)
and then apply cumsum to sections of x based onthe lengths returned by rle

Carl