This function extracts the variable part from a character vector of
predicate names. Each element of x
is expected to follow the pattern
<varname>=<value>
, where <varname>
is a variable name and <value>
is
the associated value.
Value
A character vector containing the <varname>
parts of predicate
names in x
. If an element does not contain =
, the entire string is
returned as is. If x
is NULL
, the function returns NULL
. If x
has
length zero (character(0)
), the function returns character(0)
.
Details
If an element does not contain an equal sign (=
), the entire string is
returned unchanged.
This function is the counterpart to values()
, which extracts the value
part of predicates. Together, var_names()
and values()
provide a
convenient way to split predicate strings into their variable and value
components.