[R] how to efficiently compute set unique?

[G FANG]

Hi,

I want to get the unique set from a large numeric k by 1 vector, k is
in tens of millions

when I used the matlab function unique, it takes less than 10 secs

but when I tried to use the unique in R with similar CPU and memory,
it is not done in minutes

I am wondering, am I using the function in the right way?

dim(cntxtn)
[1] 13584763        1
uniqueCntxt = unique(cntxtn);    # this is taking really long

Please advice.

Thanks,

Gang