fn real_groups(
column: SEXP,
col: &str,
) -> Result<Vec<(GroupKey, Vec<usize>)>, DataFrameError>Expand description
Double keys (plain, Date, POSIXct, other classed doubles): numeric
sort with NaN after every number, NA_real_ last. Equality follows
RealKey (-0 == 0, one NaN key); labels come from one
as.character() call over the distinct keys (real_labels).