Taking diff of character vectors

Hi:
For A, you can use head and tail but you have to add a zero the front.
For B, you can use the same function, but put it inside an sapply and run
over the columns and then cbind it back with the original dataframe.
A)
nm2 <- c(rep("SPZ8", 10), rep("SPX9", 10))
-1.0*c(0,as.numeric((head(nm2,-1) != tail(nm2,-1))))

B)
nm3 <- c(rep("GLF9", 4), rep("GLF10", 16))
matr <- cbind(nm2, nm3)
temp<-as.data.frame(sapply(1:ncol(matr), function(.col) {
-1.0*c(0,as.numeric((head(matr[,.col],-1) != tail(matr[,.col],-1))))
}))
cbind(matr,temp)



On Fri, Mar 13, 2009 at? 5:24 AM, Sergey Goriatchev wrote:

Hello, everybody

Say I have
nm1 <- c(rep(1,10), rep(0,10))
then I can do:
diff(nm1)
to see where I have shift in value

but what if I have
nm2 <- c(rep("SPZ8", 10), rep("SPX9", 10))

how can I produce the same ouput as diff(nm1) does, that is zeros
everywhere except for one place where SPZ8 changes to SPX9 (there
should be 1 there)?

What if I have a matrix of characters like that:
nm3 <- c(rep("GLF9", 4), rep("GLF10", 16))
matr <- cbind(nm2, nm3)

How can I efficiently create two more columns that contain zeros
everywhere except for place where there is shift in character values?

Thanks for help!
Sergey

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