Get a vector from a vector/list/table to be used in mapping
get_sort_var(data, var)
A vector/list/table
What to get. * For tables, the names of columns can be used. * `"{{index}}"` : This means to use the index of rows/items * `"{{name}}"` : This means to use row/item names. * `"{{value}}"` : This means to use the values in vectors or lists. Lists