set.seed(45)
require(data.table) # Latest github version
DT <- data.table(
      i1 = c(1:5, NA), 
      i2 = c(NA,6,7,8,9,10), 
      f1 = factor(sample(c(letters[1:3], NA), 6, TRUE)), 
      f2 = factor(c("z", "a", "x", "c", "x", "x"), ordered=TRUE), 
      c1 = sample(c(letters[1:3], NA), 6, TRUE), 
      d1 = as.Date(c(1:3,NA,4:5), origin="2013-09-01"), 
      d2 = as.Date(6:1, origin="2012-01-01"))
# add a couple of list cols
DT[, l1 := DT[, list(c=list(rep(i1, sample(5,1)))), by = i1]$c]
DT[, l2 := DT[, list(c=list(rep(c1, sample(5,1)))), by = i1]$c]

# id, measure as character/integer/numeric vectors
melt(DT, id=1:2, measure="f1")  ## Crashes R to desktop

sessionInfo()
#R version 3.1.2 (2014-10-31)
#Platform: x86_64-w64-mingw32/x64 (64-bit)

#locale:
#[1] LC_COLLATE=English_United Kingdom.1252 
#[2] LC_CTYPE=English_United Kingdom.1252   
#[3] LC_MONETARY=English_United Kingdom.1252
#[4] LC_NUMERIC=C                           
#[5] LC_TIME=English_United Kingdom.1252    

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

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

#loaded via a namespace (and not attached):
#[1] chron_2.3-45 tools_3.1.2