Fast concatenation of data.table columns into one string column

Question

Given an arbitrary list of column names in a data.table, I want to concatenate the contents of those columns into a single string stored in a new column. The column

Answer 1

This uses unite from package tidyr. May not be the fastest, but it is probably faster than hand-coded R code.

library(tidyr)
system.time(
  DNew <- DT %>% unite(State, ConcatCols, sep = "", remove = FALSE)
)
# user  system elapsed 
# 14.974   0.183  15.343 

DNew[1:10]
# State   x   y a b c d e f
# 1: foo211621bar foo bar 2 1 1 6 2 1
# 2: foo532735bar foo bar 5 3 2 7 3 5
# 3: foo965776bar foo bar 9 6 5 7 7 6
# 4: foo221284bar foo bar 2 2 1 2 8 4
# 5: foo485976bar foo bar 4 8 5 9 7 6
# 6: foo566778bar foo bar 5 6 6 7 7 8
# 7: foo892636bar foo bar 8 9 2 6 3 6
# 8: foo836672bar foo bar 8 3 6 6 7 2
# 9: foo963926bar foo bar 9 6 3 9 2 6
# 10: foo385216bar foo bar 3 8 5 2 1 6