使用data.table我可以执行以下操作:
library(data.table)
dt = data.table(a = 1:2, b = c(1,2,NA,NA))
# a b
#1: 1 1
#2: 2 2
#3: 1 NA
#4: 2 NA
dt[, b := b[1], by = a]
# a b
#1: 1 1
#2: 2 2
#3: 1 1
#4: 2 2
dplyr然而,尝试相同的操作,数据被加扰/排序a:
library(dplyr)
dt = data.table(a = 1:2, b = c(1,2,NA,NA))
dt %.% group_by(a) %.% mutate(b = b[1])
# a b
#1 1 1
#2 1 1
#3 2 …