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fastConcat

Hopefully allows fast concatenation of data.table columns by re-purposing some of the data.table package internals.

One trick pony with function fastConcat::concat() based off of stack overflow question Fast Concatenation of data.table columns.

  • Works, if all you want to concatenate is single digit integers for now
  • Use at your own risk! Passing in non-integers, a multi-character separator, or one of many other possible things a reasonable person might try will probably cause a segfault and crash your R session!

Note: All the elegant C code actually came from the data.table package internals.

library(fastConcat)
library(data.table)

RowCount <- 5
DT <- data.table(x = "foo",
                 y = "bar",
                 a = sample.int(9, RowCount, TRUE),
                 b = sample.int(9, RowCount, TRUE),
                 c = sample.int(9, RowCount, TRUE),
                 d = sample.int(9, RowCount, TRUE),
                 e = sample.int(9, RowCount, TRUE),
                 f = sample.int(9, RowCount, TRUE))

## Generate an expression to paste an arbitrary list of columns together
ConcatCols <- list("a","b","c","d","e","f")
## Do it 3x as many times
ConcatCols <- c(ConcatCols,ConcatCols,ConcatCols)

column_indices <- sapply(ConcatCols, FUN = function(x) { which(colnames(DT) == x )})

DT[, State := fastConcat::concat(DT, column_indices, sep = "")]
print(DT)
     x   y a b c d e f              State
1: foo bar 8 9 7 8 3 3 897833897833897833
2: foo bar 2 5 6 1 5 5 256155256155256155
3: foo bar 1 1 6 5 8 9 116589116589116589
4: foo bar 2 5 2 6 3 4 252634252634252634
5: foo bar 3 7 1 1 9 1 371191371191371191