DT[j ,c("COL1", "NEW_COL"):=list(COL2, newValue)] returns error if j does not match

[cguill95]

The below script illustrates the issue

DT <- data.table(
COL_INT = 1L,
COL_INT_2 = 5L,
)

# Works
DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(9L, "Test")]

# Does not work
DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(COL_INT_2, "Test")]

[mattdowle]

Works for me. Please follow the Support Guide (e.g. point 3) and the issue template. "Does not work" is a well known unhelpful statement, referred to in the links in those guides.

[st-pasha]

I can reproduce the error with latest data.table just pulled from master:

R version 3.4.2 (2017-09-28) -- "Short Summer"
Copyright (C) 2017 The R Foundation for Statistical Computing
Platform: x86_64-apple-darwin15.6.0 (64-bit)
...
> require(data.table)
Loading required package: data.table
data.table 1.11.1 IN DEVELOPMENT built 2018-05-03 18:45:22 UTC; pasha
  The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way
  Documentation: ?data.table, example(data.table) and browseVignettes("data.table")
  Release notes, videos and slides: http://r-datatable.com
> DT <- data.table(COL_INT=1L, COL_INT_2=5L)
> DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(COL_INT_2, "Test")]
Error in `[.data.table`(DT, COL_INT == 0L, `:=`(c("COL_INT", "NEW_COL"),  : 
  RHS of assignment to existing column 'COL_INT' is zero length but not NULL. If you intend to delete the column use NULL. Otherwise, the RHS must have length > 0; e.g., NA_integer_. If you are trying to change the column type to be an empty list column then, as with all column type changes, provide a full length RHS vector such as vector('list',nrow(DT)); i.e., 'plonk' in the new column.

I presume the operation should have been a noop, given that i matched no rows (and if i did match some rows, j would have been a valid update statement too).

[mattdowle]

Still works for me. What's the difference?

R version 3.4.4 (2018-03-15) -- "Someone to Lean On"
Copyright (C) 2018 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)
...
> require(data.table)
Loading required package: data.table
data.table 1.11.1 IN DEVELOPMENT built 2018-05-03 21:05:11.755 UTC; mdowle
  The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way
  Documentation: ?data.table, example(data.table) and browseVignettes("data.table")
  Release notes, videos and slides: http://r-datatable.com
> DT <- data.table(COL_INT=1L, COL_INT_2=5L)
> DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(9L, "Test")]
> DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(COL_INT_2, "Test")]
>

[st-pasha]

The difference is that you did DT[COL_INT == 0L, c("COL_INT", "NEW_COL"):=list(9L, "Test")] step first. Not sure why (maybe because it creates a key on COL_INT?), but it makes the following step work.

[MarkusBonsch]

Seems very much related to
#759
#2690