在 R 中，如何按组添加最大值？

Question

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

Answer 1

如果您x首先重新定义（cbind使两列都成为因子），

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

Answer 2

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