R: find largest common substring starting at the beginning

Question

I\'ve got 2 vectors:

word1 <- \"bestelling\"   
word2 <- \"bestelbon\"

Now I want to find the largest common substring that starts at the

Answer 1

This seems to work

longestprefix<-function(a,b) {
    n <- pmin(nchar(a), nchar(b))
    mapply(function(x, y, n) {
        rr<-rle(x[1:n]==y[1:n])
        if(rr$values[1]) {
            paste(x[1:rr$lengths[1]], collapse="")
        } else {
            ""
        }
    }, strsplit(a, ""), strsplit(b,""), n)
}



longestprefix("bestelling", "bestelbon")
# [1] "bestel"
longestprefix("bestelling", "stel")
# [1] ""