Sample data taken from this SO post from Douglas Clark. Thanks for the nice example!
require(data.table)
# main data table DT, keyed on site and date, with data column x
DT <- data.table(site = rep(LETTERS[1:2], each=3),
date = rep(1:3, times=2),
x = rep(1:3*10, times=2),
key = "site,date")
DT
# site date x
#1: A 1 10
#2: A 2 20
#3: A 3 30
#4: B 1 10
#5: B 2 20
#6: B 3 30
# lookup table for x to y lookup, keyed on x
x2y <- data.table(x = c(10,20), y = c(100,200), key = "x")
x2yTo join on column x, we don't have to re-key anymore:
DT[x2y, on="x"]
# site date x y
#1: A 1 10 100
#2: B 1 10 100
#3: A 2 20 200
#4: B 2 20 200
key(DT[x2y, on="x"])
# [1] "site" # <~~~ wrong
It should be x as i here is keyed on that column, and corresponding column in DT is also named x.
Sample data taken from this SO post from Douglas Clark. Thanks for the nice example!
To join on column
x, we don't have to re-key anymore:It should be
xasihere is keyed on that column, and corresponding column inDTis also namedx.