From data frame to list object

Dear all, let say I have following data frame:

data.frame(x=rnorm(18), y=rep(c("a", "b", "c"), each=6))

             x y

1  -1.072152537 a

2   0.382985265 a

3   0.058877377 a

4  -0.006911939 a

5  -2.355269051 a

6  -0.303095553 a

7   0.484038422 b

8   0.733928931 b

9  -1.136014346 b

10  0.503552090 b

11  1.708609658 b

12 -0.294599403 b

13  1.239308497 c

14  0.754081946 c

15 -0.237346858 c

16 -0.051011439 c

17 -0.618675146 c

18  0.537612359 c

From this data frame I want to create a "list" of length 3, where  
each

element of this list will be a vector corresponding to the value of  
y. For
example, 1st element will be all "x" values corresponding to the  
"y=a", and
similarly the other elements of this list. Can somebody point me how  
to do
this without having some "for" loop?



Thanks and regards,


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