R data.table segfault when trying to update one column and create another

Question

Is it possible to create a new column in a data.table and update an existing column at the same time? The following didn't work. Thanks.

library(data.table)
dt <- data.table(x=runif(4), y=runif(4), z=c("x","x","y","y"))
dt[, c("x", "y") := list(x[1], y[1]), by=z]     # works
dt[, c("x", "newx") := list(x[1], y[1]), by=z]

Caught Segfault:

address 0x20000010, cause 'memory not mapped'

Traceback:

 1: [.data.table(dt, , :=(c("x", "newx"), list(x[1], y[1])), by = z)
 2: dt[, :=(c("x", "newx"), list(x[1], y[1])), by = z]

Answer 1

Yes. But you need v1.8.9 from R-Forge to get the following fix :

o Mixing adding and updating into one DT[, :=(existingCol=...,newCol=...), by=...] now works without error or segfault, #2778 and #2528. Many thanks to Arunkumar Srinivasan for reporting and for the nice reproducible examples. Tests added.

See latest NEWS (updated live) for other changes in v1.8.9.