R: pairwise matrix of the number of characters that differ among strings

Question

I have a vector containing a large number of strings that are all of the same length. For example:

vec = c("keep", "teem", "meat", "weep")

I would like to compare every possible pair of strings from within this vector and count the number of characters that differ between them. Using the vector above, "keep" would be compared to every other string in the vector, "teem" would be compared to every other string, and so on. I'm only interested in counting the number of characters from the same position within each string that are different. So for example "keep" vs. "teem" would have 2 differences, "keep" vs. "meat" 3 differences, etc. I'd like to output the results as a pairwise matrix, where the strings in the vector make up the row names and column names.

I've learned from another post (How can I compare two strings to find the number of characters that match in R, using substitution distance?) that I can use the adist argument in mapply to calculate the number of differences between two strings:

mapply(adist,string1,string2)

But I'm not sure how to modify this to operate over every possible pairwise combination in my vector, and to place the results in a pairwise matrix. Any ideas for how to do that? Thanks!!

Answer 1

Do you mean using adist like below?

> `dimnames<-`(adist(vec),rep(list(vec),2))
     keep teem meat weep
keep    0    2    3    1
teem    2    0    3    2
meat    3    3    0    3
weep    1    2    3    0

Answer 2

An option with stringdistmatrix

library(stringdist)
out <- as.matrix(stringdistmatrix(vec))
dimnames(out) <- list(vec, vec)