Extract characters that differ between two strings

Question

I have used adist to calculate the number of characters that differ between two strings:

a <- \"Happy day\"
b <- \"Tappy Pay\"
adist(a,b)          


        

Answer 1

As long as a and b have the same length we can do this:

s.a <- strsplit(a, "")[[1]]
s.b <- strsplit(b, "")[[1]]
paste(s.a[s.a != s.b], collapse = "")

giving:

[1] "Hd"

This seems straightforward in terms of clarity of the code and seems tied for the fastest of the solutions provided here although I think I prefer f3:

f1 <- function(a, b)
  paste(setdiff(strsplit(a,"")[[1]],strsplit(b,"")[[1]]), collapse = "")

f2 <- function(a, b)
  paste(sapply(setdiff(utf8ToInt(a), utf8ToInt(b)), intToUtf8), collapse = "")

f3 <- function(a, b) 
  paste(Reduce(setdiff, strsplit(c(a, b), split = "")), collapse = "")

f4 <- function(a, b) {
  s.a <- strsplit(a, "")[[1]]
  s.b <- strsplit(b, "")[[1]]
  paste(s.a[s.a != s.b], collapse = "")
}

a <- "Happy day"
b <- "Tappy Pay"

library(rbenchmark)
benchmark(f1, f2, f3, f4, replications = 10000, order = "relative")[1:4]

giving the following on a fresh session on my laptop:

  test replications elapsed relative
3   f3        10000    0.07    1.000
4   f4        10000    0.07    1.000
1   f1        10000    0.09    1.286
2   f2        10000    0.10    1.429

I have assumed that the differences must be in the corresponding character positions. You might want to clarify if that is the intention or not.