Warning on merge: longer object length is not a multiple of shorter object length

[renkun-ken]

When I upgrade data.table to the latest release (1.11.6) from 1.11.4, the following code produces a warning:

library(data.table)
d1 <- data.table(
  S_INFO_WINDCODE = c("000001.SZ", "000001.SZ", 
    "000001.SZ", "000001.SZ", "000001.SZ"), 
  ANN_DT = c(19900321L, 19901231L, 19901231L, 19901231L, 19901231L), 
  REPORT_PERIOD = c(19891231L, 19891231L, 19900331L, 19900630L, 19900930L), 
  REPORT_YEAR = c(1989L, 1989L, 1990L, 1990L, 1990L), 
  REPORT_QUARTER = c(4L, 4L, 1L, 2L, 3L),
  key = c("S_INFO_WINDCODE", "ANN_DT", "REPORT_PERIOD"))
d2 <- data.table(
  S_INFO_WINDCODE = c("000001.SZ", "000001.SZ", 
  "000001.SZ", "000001.SZ", "000001.SZ"), 
  ANN_DT = c(19900321L, 19901231L, 19901231L, 19901231L, 19901231L), 
  REPORT_PERIOD = c(19891231L, 19891231L, 19900331L, 19900630L, 19900930L), 
  REPORT_YEAR = c(1989L, 1989L, 1990L, 1990L, 1990L), 
  REPORT_QUARTER = c(4L, 4L, 1L, 2L, 3L),
  key = c("S_INFO_WINDCODE", "ANN_DT", "REPORT_PERIOD"))
d3 <- merge(d1, d2, by = c("S_INFO_WINDCODE", "ANN_DT", "REPORT_PERIOD", "REPORT_YEAR", "REPORT_QUARTER"))

Warning message:
In head(key(i), length(leftcols)) == names(i)[leftcols] :
  longer object length is not a multiple of shorter object length

My session info:

R version 3.5.1 (2018-07-02)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS High Sierra 10.13.6

Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.5/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.11.6

loaded via a namespace (and not attached):
[1] compiler_3.5.1 tools_3.5.1   

It is reproducible under macOS + R 3.5, Ubuntu 16.04 + R 3.5, Ubuntu 16.04 + R 3.4, Ubuntu 18.04 + R 3.5.

[renkun-ken]

I did some debugging and the following code will trigger the warning

d2[d1, on = c("S_INFO_WINDCODE", "ANN_DT", "REPORT_PERIOD", "REPORT_YEAR", "REPORT_QUARTER")]

The warning happens at https://github.com/Rdatatable/data.table/blob/master/R/data.table.R#L1331

[mattdowle]

Closed by #3063