6.4 Concatenate NULL

20180720 Each operator/functions treats NULL differently. Note the convenience for base::cat() to add a space between the strings, and that backports::paste() treats NULL as a zero length string, and thus there are two spaces between the words concatenated.

"hello" %s+% NULL %s+% "world"
## character(0)
str_c("hello", NULL, "world")
## [1] "helloworld"
glue("hello", NULL, "world")
cat("hello", NULL, "world")
## hello world
paste("hello", NULL, "world")
## [1] "hello  world"

NA tends to be treated differently too.

"hello" %s+% NA %s+% "world"
## [1] NA
str_c("hello", NA, "world")
## [1] NA
glue("hello", NA, "world")
## helloNAworld
cat("hello", NA, "world")
## hello NA world
paste("hello", NA, "world")
## [1] "hello NA world"

The examples becomes more interesting in the context that the arguments to the functions might be string returning functions. If that function returns NULL or NA, purposely or accidentally then it is useful to know the consequences.

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