Lookup by column function factory.

Source: R/make_dt_lookup_by_column.R

Build data.table implementation of lookup_by_column. We do this here as rqdatatable is a data.table aware package (and rquery is not).

make_dt_lookup_by_column(pick, result)

Arguments

pick

character scalar, name of column to control value choices.
result

character scalar, name of column to place values in.

Value

f_dt() function.

Examples


df = data.frame(x = c(1, 2, 3, 4),
                y = c(5, 6, 7, 8),
                choice = c("x", "y", "x", "z"),
                stringsAsFactors = FALSE)
make_dt_lookup_by_column("choice", "derived")(df)

#>    x y choice derived
#> 1: 1 5      x       1
#> 2: 2 6      y       6
#> 3: 3 7      x       3
#> 4: 4 8      z      NA

# # base-R implementation
# df %.>% lookup_by_column(., "choice", "derived")
# # # data.table implementation (requies rquery 1.1.0, or newer)
# # df %.>% lookup_by_column(., "choice", "derived",
# #                          f_dt_factory = rqdatatable::make_dt_lookup_by_column)