[R] How do I avoid a loop?

[Erik Iverson]

One more variation on the solution, no idea how it compares in speed.

Using your x ...

 > ifelse(x, unlist(mapply(seq, to = rle(x)$lengths, from = 1)), 0)
[1] 1 2 3 0 0 1 2 0 1

Feng, Ken wrote:
> Hi,
> 
> I start with an array of booleans:
> 
> 	x <- c( TRUE, TRUE, TRUE, FALSE, FALSE, TRUE, TRUE, FALSE, TRUE );
> 
> I want to define an y <- f(x) such that:
> 
> 	y <- c( 1, 2, 3, 0, 0, 1, 2, 0, 1 );
> 
> In other words, do a cumsum when I see a TRUE, but reset to 0 if I see a FALSE.
> 
> I know I can do this with a very slow and ugly loop or maybe use apply,
> but I was hoping there are some R experts out there who can show me
> a cleaner/more elegant solution?
> 
> Thanks in advance.
> 
> - Ken
> 
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