How to extend `==` behavior to vectors that include NAs?

Question

I\'ve completely failed at searching for other r-help or Stack Overflow discussion of this specific issue. Sorry if it\'s somewhere obvious. I believe that I\'m just lo

Answer 1

Another option, but is it better than mapply('%in%', a , b)?:

(!is.na(a) & !is.na(b) & a==b) | (is.na(a) & is.na(b))

Following @AnthonyDamico 's suggestion, creation of the "mutt" operator:

"%==%" <- function(a, b) (!is.na(a) & !is.na(b) & a==b) | (is.na(a) & is.na(b))

Edit: or, slightly different and shorter version by @Frank (which is also more efficient)

"%==%" <- function(a, b) (is.na(a) & is.na(b)) | (!is.na(eq <- a==b) & eq)

With the different examples:

a <- c( 1 , 2 , 3 )
b <- c( 1 , 2 , 4 )
a %==% b
# [1]  TRUE  TRUE FALSE

a <- c( 1 , NA , 3 )
b <- c( 1 , NA , 4 )
a %==% b
# [1]  TRUE  TRUE FALSE

a <- c( 1 , NA , 3 )
b <- c( 1 , 2 , 4 )
a %==% b
#[1]  TRUE FALSE FALSE

a <- c( 1 , NA , 3 )
b <- c( 3 , NA , 1 )
a %==% b
#[1] FALSE  TRUE FALSE