Speed up this loop to create dummy columns with data.table and set in R [duplicate]

Answer 1

Here is one attempt at a speed up:

Day <- unique(dt$Week_Day)
setkey(dt, Week_Day)

# create columns of 0s
dt[, (Day) := 0L]

for (i in seq_along(head(Day, -1))) {
     dt[Day[i], Day[i] := 1L]
}

This implements a couple of the data.table speed ups including binary search in the second chain and the elimination of ifelse with replacement by reference.