tstrsplit function to strsplit *and* transpose to easily split + update columns directly.

[arunsrinivasan]

This has come up quite frequently on SO. Here is one example.

Conceptually, tstrsplit() is just transpose(strsplit(...), fill=.) where transpose() is implemented in #1025.

require(data.table)
dt <- data.table(category.tag=c("toys/David", "toys/David", "toys/James", "toys", "toys", "toys/James"), transaction=1:6)
#    category.tag transaction
#1:   toys/David           1
#2:   toys/David           2
#3:   toys/James           3
#4:         toys           4
#5:         toys           5
#6:   toys/James           6

dt[, c("category", "tag") := tstrsplit(category.tag, "/", fixed=TRUE)]
#    category.tag transaction category   tag
#1:   toys/David           1     toys David
#2:   toys/David           2     toys David
#3:   toys/James           3     toys James
#4:         toys           4     toys    NA
#5:         toys           5     toys    NA
#6:   toys/James           6     toys James

Additionally we can also pass a fill = argument to tstrsplit.

[arunsrinivasan]

Updated this and this SO posts.