shift case of crash R session

[jangorecki]

Not sure but I assume below should work. Field time_code is unique Date.
Latest master currently crash R session in the below case:

library(data.table)
DT <- data.table(
  time_code = structure(c(15436, 15437, 15438, 15439, 15440), class = "Date"),
  value = c(712242.20376462, 608841.4513506, 182544.2945119, 872201.29650086, 352442.92207062)
)
DT[, c("value_lead_2") := shift(value, n=2, fill=NA, type="lead", give.names=FALSE), by=c("time_code")]

session

R version 3.1.2 (2014-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_DK.UTF-8        LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=C             
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

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

other attached packages:
[1] data.table_1.9.5

loaded via a namespace (and not attached):
[1] bitops_1.0-6   chron_2.3-45   devtools_1.6.1 httr_0.6.1     RCurl_1.95-4.5 stringr_0.6.2  tools_3.1.2