This function powers dplyr::pull() and various functions of the
tidyr package. It is similar to vars_select() but returns only
one column name and has slightly different semantics: it allows
negative numbers to select columns from the end.
a positive integer, giving the position counting from the left
a negative integer, giving the position counting from the right.
The default returns the last column (on the assumption that's the
column you've created most recently).
This argument is taken by expression and supports
quasiquotation (you can unquote column
names and column locations).
error_call
The execution environment of a currently
running function, e.g. caller_env(). The function will be
mentioned in error messages as the source of the error. See the
call argument of abort() for more information.
error_arg
An argument name as a string. This argument
will be mentioned in error messages as the input that is at the
origin of a problem.
# It takes its argument by expression:vars_pull(letters, c)
# Negative numbers select from the end:vars_pull(letters, -3)
# You can unquote variables:var <- 10
vars_pull(letters, !!var)