更新时间:2023-01-21 18:10:01
data.table
$ c> unique ,重复
和 anyDuplicated
unique(dt,by = c('x','y'))
会给你想要的。
I'd like to get the first row only from a data.table, grouped by multiple columns.
This is straightforward with a single column, e.g.:
(dt <- data.table(x = c(1, 1, 1, 2),
y = c(1, 1, 2, 2),
z = c(1, 2, 1, 2)))
# x y z
# |1: 1 1 1
# |2: 1 1 2
# |3: 1 2 1
# |4: 2 2 2
dt[!duplicated(x)] # Remove rows 2-3
# x y z
# |1: 1 1 1
# |2: 2 2 2
But none of these approaches work when trying to remove based on two columns; i.e. in this case removing only row 2:
dt[!duplicated(x, y)] # Keeps only original data set
# x y z
# |1: 1 1 1
# |2: 1 1 2
# |3: 1 2 1
# |4: 2 2 2
dt[!duplicated(list(x, y))] # Same as above
dt[!duplicated(c("x", "y"))] # Same as above
dt[!duplicated(list("x", "y"))] # Same as above
dt[!duplicated(c(x, y))] # Only removes duplicates from first column
# x y z
# |1: 1 1 1
# |2: 2 2 2
Except for this, which only works in certain cases:
dt[!duplicated(paste0(x, y))]
# x y z
# |1: 1 1 1
# |2: 1 2 1
# |3: 2 2 2
data.table
provides S3 methods for unique
, duplicated
and anyDuplicated
unique(dt, by = c('x','y'))
will give you what you want.