根据dplyr帮助文件,该sample_n功能每组采样固定数量.
当我运行以下代码时,我希望每个tobgp和alcgp组合有两个样本,所以总共有32(4*4*2)行.但是只返回两行.
by_tobgp_alcgp <- esoph %>% group_by(tobgp,alcgp)
sample_n(by_tobgp_alcgp , 2)
# Source: local data frame [2 x 5]
# Groups: tobgp, alcgp
#
# agegp alcgp tobgp ncases ncontrols
# 10 25-34 80-119 10-19 0 1
# 50 55-64 0-39g/day 30+ 4 6
它是否正确？有没有其他方法可以实现这一目标dplyr？
所述sample_n操作者将工作在分组的数据帧为dplyr版本> = 0.3
library(dplyr)
data(esoph)
set.seed(123)
esoph %>%
group_by(tobgp, alcgp) %>%
sample_n(2)
#Source: local data frame [32 x 5]
#Groups: tobgp, alcgp [16]
#
#agegp alcgp tobgp ncases ncontrols
#(fctr) (fctr) (fctr) (dbl) (dbl)
#1 65-74 0-39g/day 0-9g/day 5 48
#2 25-34 0-39g/day 0-9g/day 0 40
#3 45-54 40-79 0-9g/day 6 38
#4 75+ 40-79 0-9g/day 2 5
#5 55-64 80-119 0-9g/day 9 18
#6 35-44 80-119 0-9g/day 0 11
#7 45-54 120+ 0-9g/day 4 4
#8 65-74 120+ 0-9g/day 3 4
#9 45-54 0-39g/day 10-19 0 18
#10 65-74 0-39g/day 10-19 4 14
#11 75+ 40-79 10-19 1 3
#12 55-64 40-79 10-19 6 21
#13 45-54 80-119 10-19 6 14
#14 25-34 80-119 10-19 0 1
#15 75+ 120+ 10-19 1 1
#16 35-44 120+ 10-19 0 3
#17 25-34 0-39g/day 20-29 0 6
#18 55-64 0-39g/day 20-29 3 12
#19 65-74 40-79 20-29 5 9
#20 25-34 40-79 20-29 0 4
#21 55-64 80-119 20-29 3 6
#22 65-74 80-119 20-29 2 3
#23 45-54 120+ 20-29 2 3
#24 35-44 120+ 20-29 2 4
#25 55-64 0-39g/day 30+ 4 6
#26 35-44 0-39g/day 30+ 0 8
#27 35-44 40-79 30+ 0 8
#28 25-34 40-79 30+ 0 7
#29 35-44 80-119 30+ 0 1
#30 55-64 80-119 30+ 4 4
#31 25-34 120+ 30+ 0 2
#32 65-74 120+ 30+ 1 1
您可以使用do运算符解决此问题:
library(dplyr)
data(esoph)
esoph %>%
group_by(tobgp, alcgp) %>%
do(sample_n(., 2))
# agegp alcgp tobgp ncases ncontrols
#1 75+ 0-39g/day 0-9g/day 1 18
#2 35-44 0-39g/day 0-9g/day 0 60
#3 55-64 40-79 0-9g/day 9 40
#4 75+ 40-79 0-9g/day 2 5
#5 65-74 80-119 0-9g/day 6 13
#6 55-64 80-119 0-9g/day 9 18
#7 65-74 120+ 0-9g/day 3 4
#8 25-34 120+ 0-9g/day 0 1
#9 25-34 0-39g/day 10-19 0 10
#10 35-44 0-39g/day 10-19 1 14
#11 65-74 40-79 10-19 3 10
#12 55-64 40-79 10-19 6 21
#13 55-64 80-119 10-19 8 15
#14 35-44 80-119 10-19 0 6
#15 25-34 120+ 10-19 1 1
#16 35-44 120+ 10-19 0 3
#17 25-34 0-39g/day 20-29 0 6
#18 35-44 0-39g/day 20-29 0 7
#19 45-54 40-79 20-29 5 15
#20 75+ 40-79 20-29 0 3
#21 65-74 80-119 20-29 2 3
#22 45-54 80-119 20-29 1 5
#23 55-64 120+ 20-29 2 3
#24 45-54 120+ 20-29 2 3
#25 25-34 0-39g/day 30+ 0 5
#26 55-64 0-39g/day 30+ 4 6
#27 25-34 40-79 30+ 0 7
#28 75+ 40-79 30+ 1 1
#29 55-64 80-119 30+ 4 4
#30 35-44 80-119 30+ 0 1
#31 55-64 120+ 30+ 5 6
#32 25-34 120+ 30+ 0 2
评论后编辑:
对于组数据,do操作员将函数应用于在这种情况下所需的每组数据(选择每组的大小为2的样本).因此虽然sample_n不能对分组数据起作用(不确定它是否应该,但我认为它应该有效),使用do(sample_n(data,n))可以根据需要完成工作.