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

A little messy, but it's what I came up with:

largest_subset <- Vectorize(function(word1,word2) {
    substr(word1, 1, sum(substring(word1, 1, 1:nchar(word1))==substring(word2, 1, 1:nchar(word2))))
})

It produces a warning message if the words are not the same length, but have no fear. It checks to see if each substring from the first character of each word to every position produces a match between the two words. You can then count how many values came out to be true, and capture the substring up to that character. I vectorized it so you can apply it to word vectors.

> word1 <- c("tester","doesitwork","yupyppp","blanks")
> word2 <- c("testover","doesit","yupsuredoes","")
> largest_subset(word1,word2)
    tester doesitwork    yupyppp     blanks 
    "test"   "doesit"      "yup"         ""