[R] comparing elements in a vector

[Peter Dalgaard BSA]

Sven Garbade <garbade at psy.uni-muenchen.de> writes:

> Hi all,
> 
> there is a vector d which contains three different valus: 0, 1 or 2. I
> wrote a loop which gives me T, when the values in d changed from 1 to
> 2 or from 2 to 1, otherwise F:
> 
> for(i in 1:(length(d)-1)) {
>    if(d[i] != d[i+1] & d[i] != 0 & d[i+1] != 0)
>       change[i+1] <- T	    
>     else	  
>       change[i+1] <- F
> }
> 
> This works, but I'm wondering if there is already a R function or an
> easier way to avoid the for-loop.

& and friends vectorize, so

# testdata:
d <- rbinom(30,2,.5)

N <- length(d)
d1 <- d[-N]
d2 <- d[-1]
change <- (d1 != d2) & d1 & d2
# and, just to print and check:
data.frame(d,change=c(NA,change))


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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