parse_expr {rlang} | R Documentation |
These functions parse and transform text into R expressions. This is the first step to interpret or evaluate a piece of R code written by a programmer.
parse_expr(x) parse_exprs(x)
x |
Text containing expressions to parse_expr for
|
parse_expr()
returns one expression. If the text contains more
than one expression (separated by semicolons or new lines), an error is
issued. On the other hand parse_exprs()
can handle multiple
expressions. It always returns a list of expressions (compare to
base::parse()
which returns a base::expression vector). All
functions also support R connections.
parse_expr()
returns an expression,
parse_exprs()
returns a list of expressions. Note that for the
plural variants the length of the output may be greater than the
length of the input. This would happen is one of the strings
contain several expressions (such as "foo; bar"
). The names of
x
are preserved (and recycled in case of multiple expressions).
# parse_expr() can parse any R expression: parse_expr("mtcars %>% dplyr::mutate(cyl_prime = cyl / sd(cyl))") # A string can contain several expressions separated by ; or \n parse_exprs("NULL; list()\n foo(bar)") # Use names to figure out which input produced an expression: parse_exprs(c(foo = "1; 2", bar = "3")) # You can also parse source files by passing a R connection. Let's # create a file containing R code: path <- tempfile("my-file.R") cat("1; 2; mtcars", file = path) # We can now parse it by supplying a connection: parse_exprs(file(path))