extracting row labels (?) from a data.frame

Question

Starting with a data.frame...

df = data.frame(k=c(1,5,4,7,6), v=c(3,1,4,1,5))
> df
  k v
1 1 3
2 5 1
3 4 4
4 7 1
5 6 5

I might run some number of arbitrary manipulations...

> foo1 = df[df$k>3,]
> foo2 = head(foo1[order(foo1$v),], 2)
> foo2
  k v
2 5 1
4 7 1

At this point foo2 has somehow retained the original row numbers from df (in this case 2 and 4).

How do I extract these?

> insert_magic_function_here(foo2)
[1] 2 4

Answer 1

我认为你正在寻找rownames 。