【3.3.6】R保留有重复数据的

> df<-data.frame(col1=c(rep("a",3),"b","c",rep("d",3)),col2=c("A","B","C",rep("A",3),"B","C"),col3=c(3,3,1,4,4,3,2,1))
> 
> df
  col1 col2 col3
1    a    A    3
2    a    B    3
3    a    C    1
4    b    A    4
5    c    A    4
6    d    A    3
7    d    B    2
8    d    C    1
> subset(df,duplicated(col1))
  col1 col2 col3
2    a    B    3
3    a    C    1
7    d    B    2
8    d    C    1
> subset(df,duplicated(col1) | duplicated(col1, fromLast=TRUE))
  col1 col2 col3
1    a    A    3
2    a    B    3
3    a    C    1
6    d    A    3
7    d    B    2
8    d    C    1