Linux etc.

I don’t know the first thing about programming, but sometimes you see something and appreciate how elegant it is. This small solution from r-help is a good example. Someone wanted, given a vector c('p','p','t','t','t','p','k','t') to produce NA NA 1 2 3

test <- c('p','p','t','t','t','p','k','t')
v <- cumsum(ind <- test == 't')
v[!ind] <- NA

I didn't know you could assign something to an object and use it at the same time. Very neat. So if you wanted this all at once, you could also do:

v <- ifelse(cumsum(ind <- test=='t')==0,NA,cumsum(ind))

or

ifelse((v <- cumsum(test=='t'))==0,NA,v)

Maybe Dimitris' solution is in fact preferred for R, using indexing instead of if/ else, but I don't know enough about R to know whether that makes a difference.

This entry was posted on Thursday, November 5th, 2009 at 15:48 and is filed under R. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.