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

a <- "Happy day"
b <- "Tappy Pay"
adist(a,b) # result 2

Now I would like to extract those character that differ. In my example, I would like to get the string "Hd" (or "TP", it doesn't matter).

I tried to look in adist, agrep and stringi but found nothing.