Using match inside i data .table

Question

The operator %in%is a wrapper for the matching function that returns a "vector of the same length as x". For instance:

> match(c("a", "b", "c"), c("a", "a"), nomatch = 0) > 0
## [1]  TRUE FALSE FALSE

When used in idata tables, however

(dt1 <- data.table(v1 = c("a", "b", "c"), v2 = "dt1"))
   v1  v2
1:  a dt1
2:  b dt1
3:  c dt1
(dt2 <- data.table(v1 = c("a", "a"), v2 = "dt2"))
   v1  v2
1:  a dt2
2:  a dt2
dt1[v1 %in% dt2$v1]
   v1  v2
1:  a dt1
2:  a dt1

Copies Received

. If the expected behavior %in%inside the i.table data does not produce the same result as

dt1[dt1$v1 %in% dt2$v1]  
   v1  v2
1:  a dt1

i.e. no duplicates?

Answer 1

It was a mistake in data.tableV <1.9.5 automatic indexing, fixed in V> = 1.9.5.

I can think of three possible workarounds:

• Turn off automatic indexing and use the R base %in%, as in

  options(datatable.auto.index = FALSE)
  dt1[v1 %in% dt2$v1]
  ##    v1  v2
  ## 1:  a dt1
  

• %chin%, ( )

  dt1[v1 %chin% dt2$v1]
  ##    v1  v2
  ## 1:  a dt1
  

• Github ( R )

  library(devtools)
  install_github("Rdatatable/data.table", build_vignettes = FALSE)
  library(data.table)
  dt1 <- data.table(v1 = c("a", "b", "c"), v2 = "dt1")
  dt2 <- data.table(v1 = c("a", "a"), v2 = "dt2")
  dt1[v1 %in% dt2$v1]
  ##    v1  v2
  ## 1:  a dt1