Check if an element of a pairlist is missing.

missing_arg(arg)

Arguments

arg

the object to test.

Details

The argument passed to missing_arg is typically an element of a pairlist or the list produced by alist(). missing_arg returns TRUE if it is missing and FALSE otherwise.

Objects of type pairlist come up at R level almost exclusively as the formal arguments of functions. missing_arg can be useful when they are manipulated programmatically.

Value

TRUE or FALSE

Examples

lmargs <- formals(lm) class(lmargs) # pairlist
#> [1] "pairlist"
missing_arg(lmargs$data)
#> [1] TRUE
## which arguments of lm() have no (explicit) defaults? sapply(lmargs, missing_arg)
#> formula data subset weights na.action method #> TRUE TRUE TRUE TRUE TRUE FALSE #> model x y qr singular.ok contrasts #> FALSE FALSE FALSE FALSE FALSE FALSE #> offset ... #> TRUE TRUE
## This gives an error: ## pairlist(x = 3, y = , z = 5) ## an example with alist() pl2 <- alist(a = "", b = , c = 3) class(pl2) # list
#> [1] "list"
## this shows that 'b' is missing, 'a' and 'c' are not: sapply(pl2, missing_arg) # FALSE TRUE FALSE
#> a b c #> FALSE TRUE FALSE
## superficially, 'b' is equal to the empty string: pl2[[2]]
#>
sapply(pl2, function(x) x == "") # TRUE TRUE FALSE
#> a b c #> TRUE TRUE FALSE
## with pairlist the results are the same: g <- function(a = "", b, c = 3) NULL a.g <- formals(g) class(a.g) # pairlist
#> [1] "pairlist"
sapply(a.g, missing_arg) # FALSE TRUE FALSE
#> a b c #> FALSE TRUE FALSE
a.g[[2]]
#>
sapply(a.g, function(x) x == "") # TRUE TRUE FALSE
#> a b c #> TRUE TRUE FALSE