Extract variable names from predicate names

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.

Usage

var_names(x)

Arguments

x: A character vector of predicate names.

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.

Author

Michal Burda

Examples

var_names(c("a=1", "a=2", "b=x", "b=y"))
#> [1] "a" "a" "b" "b"
# returns c("a", "a", "b", "b")

var_names(c("a", "b=3"))
#> [1] "a" "b"
# returns c("a", "b")

var_names(character(0))
#> character(0)
# returns character(0)

var_names(NULL)
#> NULL
# returns character(0)