R data.table合并表按多列分组

Question

I have two huge data tables ( dt1 and dt2 ) that are almost identical except for 1 column. I want to join the tables by the p-1 columns, where p <- ncol(dt1) . Should I setkey() to the p-1 columns and join using dt1[dt2] ? If that is the case, how can I enter the arguments in setkey() since I can't put quoted string as argument.

Here is some simulated data:

dt1 <- data.table(matrix(rnorm(260), 10, 26))
setnames(dt1, letters)
dt2 <- copy(dt1)
dt2[,z:=rnorm(10)]

## Sections below won't run
setkey(dt1, get(letters[-which(letters=="z")]))
setkey(dt2, get(letters[-which(letters=="z")]))
dt1[dt2]

Answer 1

Use setkeyv :

setkeyv(dt1, letters[-which(letters=="z")])
setkeyv(dt2, letters[-which(letters=="z")])
dt1[dt2]

Answer 2

If you know the name of the different column this works

merge(dt1,dt2,names(dt1)[-grep("z",names(dt1))])

It also preserves the two original differing columns as dt$zx and dt$zy