我有一个data.table,其中有两列是矢量列表。
x y z
1: 1 1,2,3 8, 9,10
2: 2 5,6 3
3: 3 18,19 1,2
我希望通过一个向量列表(z`)进行拉伸和取消列表,但相应地保留并重复另一列是向量列表。我saw how to almost do this但收到错误,如下所示:
library(data.table)
dat <- data.frame(
x = 1:3,
stringsAsFactors = FALSE
)
dat[['y']] <- list(1:3, 5:6, 18:19)
dat[['z']] <- list(8:10, 3, 1:2)
setDT(dat)
# inefficient way to get what I want
a <- unlist(dat[['z']])
dat <- dat[rep(1:nrow(dat), sapply(z, length)), ]
dat[['z']] <- a
dat
x y z
1: 1 1,2,3 8
2: 1 1,2,3 9
3: 1 1,2,3 10
4: 2 5,6 3
5: 3 18,19 1
6: 3 18,19 2
# trying to do this the data.table way
# Works but dropped column
dat[, .(z = as.integer(unlist(z))), by = .(x)]
# does not work (gives error)
dat[, .(z = as.integer(unlist(z))), by = .(x, y)]
Error in `[.data.table`(dat, , .(z = as.integer(unlist(z))), by = .(x, :
column or expression 2 of 'by' or 'keyby' is type list. Do not quote column names. Usage: DT[,sum(colC),by=list(colA,month(colB))]
答案 0 :(得分:6)
只需将y
列添加到j-expression
:
dat[, .(y, z = as.integer(unlist(z))), by = x]
# x y z
#1: 1 1,2,3 8
#2: 1 1,2,3 9
#3: 1 1,2,3 10
#4: 2 5,6 3
#5: 3 18,19 1
#6: 3 18,19 2