string functions

Maybe I don't understand the question. I can think of four ways to
count, none of which give me 7:

a <- "Hello World"
b <- "Hello Peter"

#counting duplicates and the space:
sa <- strsplit(a, split="")[[1]]
sb <- strsplit(b, split="")[[1]]
length(which(sb %in% sa == TRUE))

#counting the space but not the duplicates:
sa <- unique(strsplit(a, split="")[[1]])
sb <- unique(strsplit(b, split="")[[1]])
length(which(sb %in% sa == TRUE))

#counting the duplicates but not the space:
sa <- strsplit(a, split="")[[1]]
sa <- sa[-which(sa == " ")]
sb <- strsplit(b, split="")[[1]]
sb <- sb[-which(sb ==" ")]
length(which(sb %in% sa == TRUE))

#not counting duplicates or the space:
sa <- unique(sa)
sb <- unique(sb)
length(which(sb %in% sa == TRUE))

What am I missing?

Hi!
Does anybody know a string function that would calculate how many characters
two strings share? I.e. ("Hello World","Hello Peter") would be 7.
Thanks.
Laetitia

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Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org