dtjoin_semi: Semi-join of `DT` in a `DT[i]`-style join of data frame-like objects

Description

Write (and optionally run) data.table code to return the semi-join of DT (the rows of DT that join with i) using a generalisation of DT[i] syntax.

The functions fjoin_left_semi and fjoin_right_semi provide a more conventional interface that is recommended over dtjoin_semi for most users and cases.

Usage

dtjoin_semi(
  .DT = NULL,
  .i = NULL,
  on,
  match.na = FALSE,
  mult = "all",
  mult.DT = "all",
  nomatch = NULL,
  nomatch.DT = NULL,
  select = NULL,
  do = !(is.null(.DT) && is.null(.i)),
  show = !do,
  verbose = FALSE,
  ...
)

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.
on: A character vector of join predicates, e.g. c("id", "col_DT == col_i", "date < date", "cost <= budget"), or else NA for a natural join (an equality join on all same-named columns).
match.na: If TRUE, allow equality matches between NAs or NaNs. Default FALSE.
mult: (as in [.data.table) When a row of .i has multiple matching rows in .DT, which to accept. One of "all" (the default), "first", or "last".
mult.DT: Permitted for consistency with dtjoin but has no effect on the resulting semi-join.
nomatch, nomatch.DT: Permitted for consistency with dtjoin but have no effect on the resulting semi-join.
select: Character vector of columns of .DT to be selected. NULL (the default) selects all columns. Join columns are always selected.
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.
verbose: (passed to [.data.table) Whether data.table should print information to the console during execution. Default FALSE.
...: Further arguments (for internal use).

Details

Details are as for dtjoin except for arguments controlling the order and prefixing of output columns, which do not apply.

Examples

Run this code

# Mock joins

dtjoin_semi(on = "id")
dtjoin_semi(on = c("id", "date <= date"))
dtjoin_semi(on = c("id", "date <= date"), mult = "last")