我想使用 R 在我的数据集中创建一个新列，其中包含每个唯一组的最大值。我的数据如下所示：
group<-c("A","A","A","A","A","B","B","C","C","C")
replicate<-c(1,2,3,4,5,1,2,1,2,3)
x<-data.frame(cbind(group,replicate))
我想创建如下所示的第三列 - 每个组的最大值。
group replicate max.per.group
A 1 5
A 2 5
A 3 5
A 4 5
A 5 5
B 1 2
B 2 2
C 1 3
C 2 3
C 3 3
如果您x首先重新定义（cbind使两列因素），
x<-data.frame(group,replicate)
你可以使用这个：
merge(x,aggregate(replicate~group,x,FUN=max),all.x=TRUE,by="group")
group replicate.x replicate.y
1 A 1 5
2 A 2 5
3 A 3 5
4 A 4 5
5 A 5 5
6 B 1 2
7 B 2 2
8 C 1 3
9 C 2 3
10 C 3 3
尝试
# This is how you create your data.frame
group<-c("A","A","A","A","A","B","B","C","C","C")
replicate<-c(1,2,3,4,5,1,2,1,2,3)
x<-data.frame(group,replicate) # here you don't need c()
# Here's my solution
Max <- tapply(x$replicate, x$group,max)
data.frame(x, max.per.group=rep(Max, table(x$group)))
group replicate max.per.group
1 A 1 5
2 A 2 5
3 A 3 5
4 A 4 5
5 A 5 5
6 B 1 2
7 B 2 2
8 C 1 3
9 C 2 3
10 C 3 3
这是另一个基本 R 解决方案：
cbind(x, cummax=unlist(tapply(x$replicate, x$group, function(x) rep(max(x), length(x)))))
group replicate cummax
A1 A 1 5
A2 A 2 5
A3 A 3 5
A4 A 4 5
A5 A 5 5
B1 B 1 2
B2 B 2 2
C1 C 1 3
C2 C 2 3
C3 C 3 3
共享的可重现示例建议您将列作为因子。我们需要先将它们转换为数字。
我们可以尝试使用 base R ave。找出每组中的最大值。
x$max.per.group <- ave(x$replicate, x$group, FUN = function(x) max(as.numeric(x)))
# group replicate max.per.group
#1 A 1 5
#2 A 2 5
#3 A 3 5
#4 A 4 5
#5 A 5 5
#6 B 1 2
#7 B 2 2
#8 C 1 3
#9 C 2 3
#10 C 3 3
另一种选择dplyr
library(dplyr)
x %>%
group_by(group) %>%
mutate(max.per.group = max(as.numeric(replicate)))
你可以使用这个plyr包：
library(plyr)
> ddply(x, .(group), transform, max.per.group=max(replicate))
group replicate max.per.group
1 A 1 5
2 A 2 5
3 A 3 5
4 A 4 5
5 A 5 5
6 B 1 2
7 B 2 2
8 C 1 3
9 C 2 3
10 C 3 3
>
你可以使用rle-Run Length Encoding
# Create the data.frame
group <- c("A","A","A","A","A","B","B","C","C","C")
replicate <- c(1,2,3,4,5,1,2,1,2,3)
x <- data.frame(group,replicate)
# using 'rle'
z <- rle(as.numeric(x$group))$lengths
x$max.per.group <- rep(z, z)
x
我们可以使用data.table赋值（:=）在原地创建一列，无需复制
library(data.table)
setDT(x)[, max.per.group := max(replicate), by = group]
x
# group replicate max.per.group
#1: A 1 5
#2: A 2 5
#3: A 3 5
#4: A 4 5
#5: A 5 5
#6: B 1 2
#7: B 2 2
#8: C 1 3
#9: C 2 3
#10: C 3 3
x <- data.frame(group,replicate)