f_eval_rhs | R Documentation |
f_eval_rhs
evaluates the RHS of a formula and f_eval_lhs
evaluates the LHS. f_eval
is a shortcut for f_eval_rhs
since
that is what you most commonly need.
f_eval_rhs(f, data = NULL) f_eval_lhs(f, data = NULL) f_eval(f, data = NULL) find_data(x)
f |
A formula. Any expressions wrapped in |
data |
A list (or data frame). |
x |
An object for which you want to find associated data. |
If data
is specified, variables will be looked for first in this
object, and if not found in the environment of the formula.
When used with data
, f_eval
provides two pronouns to make it
possible to be explicit about where you want values to come from:
.env
and .data
. These are thin wrappers around .data
and .env
that throw errors if you try to access non-existent values.
f_eval(~ 1 + 2 + 3) # formulas automatically capture their enclosing environment foo <- function(x) { y <- 10 ~ x + y } f <- foo(1) f f_eval(f) # If you supply data, f_eval will look their first: f_eval(~ cyl, mtcars) # To avoid ambiguity, you can use .env and .data pronouns to be # explicit: cyl <- 10 f_eval(~ .data$cyl, mtcars) f_eval(~ .env$cyl, mtcars) # Imagine you are computing the mean of a variable: f_eval(~ mean(cyl), mtcars) # How can you change the variable that's being computed? # The easiest way is "unquote" with uq() # See ?f_interp for more details var <- ~ cyl f_eval(~ mean( uq(var) ), mtcars)
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