best way to transpose data.table

The current docs show a builtin transpose method.

Specifically, you can do:

transpose(mydata, keep.names = "col", make.names = "col0")
##     col row1 row2 row3
## 1: col1   11   21   31
## 2: col2   12   22   32
## 3: col3   13   23   33

Why not just melt and dcast the data.table?

require(data.table)

dcast(melt(mydata, id.vars = "col0"), variable ~ col0)
#    variable row1 row2 row3
# 1:     col1   11   21   31
# 2:     col2   12   22   32
# 3:     col3   13   23   33

Here's an alternative solution that only uses data.table and that is closer to the original idea of using t to transpose.

mydata[, data.table(t(.SD), keep.rownames=TRUE), .SDcols=-"col0"]
##      rn V1 V2 V3
## 1: col1 11 21 31
## 2: col2 12 22 32
## 3: col3 13 23 33

If keeping the rownames is important, setnames can be used. Admittedly this becomes a bit clumsy and probably the recast solution is preferable.

setnames(mydata[, data.table(t(.SD), keep.rownames=TRUE), .SDcols=-"col0"], 
         mydata[, c('rn', col0)])[]
##      rn row1 row2 row3
## 1: col1   11   21   31
## 2: col2   12   22   32
## 3: col3   13   23   33

df <- as.data.frame(t(mydata))

is what I tried and df is a data.frame and the column names on mydata are now row names on df