dtjoin_cross: Cross join of data frame-like objects `DT` and `i` using a `DT[i]`-style interface to data.table

Description

Write (and optionally run) data.table code to return the cross join of two data.frame-like objects using a generalisation of DT[i] syntax.

The function fjoin_cross provides a more conventional interface that is recommended over dtjoin_cross for most users and cases.

Usage

dtjoin_cross(
  .DT = NULL,
  .i = NULL,
  select = NULL,
  select.DT = NULL,
  select.i = NULL,
  i.home = FALSE,
  i.first = i.home,
  prefix = if (i.home) "x." else "i.",
  i.class = i.home,
  do = !(is.null(.DT) && is.null(.i)),
  show = !do,
  ...
)

Value

A data.frame, data.table, (grouped) tibble, sf, or sf-tibble, or else NULL if do is FALSE. See Details.

Arguments

.DT, .i: data.frame-like objects (plain, data.table, tibble, sf, list, etc.), or else both omitted for a mock join statement with no data.
select, select.DT, select.i: Character vectors of columns to be selected from either input if present (select) or specifically from one or other (select.DT, select.i). NULL (the default) selects all columns. Use "" or NA to select no columns. Join columns are always selected. See Details.
i.home: Whether to treat .i as the "home" table and .DT as the "foreign" table for column prefixing and indicate. Default FALSE, i.e. .DT is the "home" table, as in [.data.table.
i.first: Whether to place .i's columns before .DT's in the join result. The default is to use the value of i.home, i.e. bring .i's columns to the front if .i is the "home" table.
prefix: A prefix to attach to column names in the "foreign" table that are the same as a column name in the "home" table. The default is "i." if the "foreign" table is .i (i.home is FALSE) and "x." if it is .DT (i.home is TRUE).
i.class: Whether the class of the output should be based on .i instead of .DT. The default follows i.home (default FALSE). See Details for how output class and other attributes are set.
do: Whether to execute the join. Default is TRUE unless .DT and .i are both omitted/NULL, in which case a mock join statement is produced.
show: Whether to print the code for the join to the console. Default is the opposite of do. If .DT and .i are both omitted/NULL, mock join code is displayed.
...: Further arguments (for internal use).

Details

Details are as for dtjoin except for remarks about join columns and matching logic, which do not apply.

Examples

Run this code

# data frames
df1 <- data.table::fread(data.table = FALSE, input = "
bread    kcal
Brown     150
White     180
Baguette  250
")

df2 <- data.table::fread(data.table = FALSE, input = "
filling kcal
Cheese   200
Pâté     160
")

dtjoin_cross(df1, df2)