R: Examples for 'rlang::call

### ** Examples

call <- quote(mean(x, na.rm = TRUE))

# Modify an existing argument
call_modify(call, na.rm = FALSE)

mean(x, na.rm = FALSE)

call_modify(call, x = quote(y))

mean(x, na.rm = TRUE, x = y)

# Remove an argument
call_modify(call, na.rm = zap())

mean(x)

# Add a new argument
call_modify(call, trim = 0.1)

mean(x, na.rm = TRUE, trim = 0.1)

# Add an explicit missing argument:
call_modify(call, na.rm = )

mean(x, na.rm = )

# Supply a list of new arguments with `!!!`
newargs <- list(na.rm = NULL, trim = 0.1)
call <- call_modify(call, !!!newargs)
call

mean(x, na.rm = NULL, trim = 0.1)

# Remove multiple arguments by splicing zaps:
newargs <- rep_named(c("na.rm", "trim"), list(zap()))
call <- call_modify(call, !!!newargs)
call

mean(x)

# Modify the `...` arguments as if it were a named argument:
call <- call_modify(call, ... = )
call

mean(x, ...)

call <- call_modify(call, ... = zap())
call

mean(x)

# When you're working with a user-supplied call, standardise it
# beforehand in case it includes unmatched arguments:
user_call <- quote(matrix(x, nc = 3))
call_modify(user_call, ncol = 1)

matrix(x, nc = 3, ncol = 1)

# `call_match()` applies R's argument matching rules. Matching
# ensures you're modifying the intended argument.
user_call <- call_match(user_call, matrix)
user_call

matrix(data = x, ncol = 3)

call_modify(user_call, ncol = 1)

matrix(data = x, ncol = 1)

# By default, arguments with the same name are kept. This has
# subtle implications, for instance you can move an argument to
# last position by removing it and remapping it:
call <- quote(foo(bar = , baz))
call_modify(call, bar = NULL, bar = missing_arg())

foo(bar = , baz)

# You can also choose to keep only the first or last homonym
# arguments:
args <-  list(bar = NULL, bar = missing_arg())
call_modify(call, !!!args, .homonyms = "first")

foo(bar = NULL, baz)

call_modify(call, !!!args, .homonyms = "last")

foo(bar = , baz)

Examples for 'rlang::call_modify'

Modify the arguments of a call