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

Source: R/dtjoin_semi.R
dtjoin_semi.Rd

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,
  ...
)

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).

Value

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

Details

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

See also

See the package-level documentation fjoin for related functions.

Examples

# Mock joins

dtjoin_semi(on = "id")
#> .DT : (unnamed)
#> .i  : (unnamed)
#> Join: na.omit(.DT, cols = "id")[id %in% .i$id]
#> 
dtjoin_semi(on = c("id", "date <= date"))
#> .DT : (unnamed)
#> .i  : (unnamed)
#> Join: setDT(.i[, na.omit(.SD), .SDcols = c("id", "date")][.DT, on = c("id", "date >= date"), nomatch = NULL, mult = "first", data.frame(id = i.id, date = i.date, col_DT, col_c = i.col_c)])[]
#> 
dtjoin_semi(on = c("id", "date <= date"), mult = "last")
#> .DT : (unnamed)
#> .i  : (unnamed)
#> Join: .DT[fsort(as.numeric(unique(.DT[.i[, na.omit(.SD), .SDcols = c("id", "date")], on = c("id", "date <= date"), nomatch = NULL, mult = "last", which = TRUE])))]
#>