I would expect set(x, i, j, val) to work similarly to x[i, j := val] or x[i, j] <- val for integer i. However, there is a discrepancy when i is 0L: While <- and := add missing columns, set() does not.
x <- data.table(a = 1)
x[0L, "b"] <- character(0)
x
#> a b
#> <num> <char>
#> 1: 1 <NA>
x <- data.table(a = 1)
x[0L, b := character(0)]
x
#> a b
#> <num> <char>
#> 1: 1 <NA>
vs.
x <- data.table(a = 1)
set(x, 0L, "b", character(0))
x
#> a
#> <num>
#> 1: 1
sessionInfo()
R version 4.1.3 (2022-03-10)
Platform: x86_64-redhat-linux-gnu (64-bit)
Running under: Fedora Linux 35 (Thirty Five)
Matrix products: default
BLAS/LAPACK: /usr/lib64/libflexiblas.so.3.2
locale:
[1] LC_CTYPE=en_US.utf8 LC_NUMERIC=C
[3] LC_TIME=en_US.utf8 LC_COLLATE=en_US.utf8
[5] LC_MONETARY=en_US.utf8 LC_MESSAGES=en_US.utf8
[7] LC_PAPER=en_US.utf8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.utf8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] data.table_1.14.3
loaded via a namespace (and not attached):
[1] compiler_4.1.3 tools_4.1.3
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I would expect set(x, i, j, val) to work similarly to x[i, j := val] or x[i, j] <- val for integer i. However, there is a discrepancy when i is 0L: While <- and := add missing columns, set() does not.
vs.
sessionInfo()