unique columns of a matrix

Dear all,

I have a matrix of repeating columns in R, for example a matrix X is

          [,1]   [,2]   [,3]   [,4]
[1,]       1      1      1      1
[2,]       1      1      2      2

I want to store unique columns of the matrix X in a new matrix Y. 
Therefore, Y will be

          [,1]   [,2]  
[1,]       1      1    
[2,]       1      2

It will be really appreciated if you can provide me some function for 
this job.
Thanks for your time and effort in advance,
Roman

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Roman Akhter Ahmed (Ph.D. Candidate)
Department of Econometrics and Business Statistics
Room 659, Building 11 (East Wing), Clayton Campus
Monash University, Victoria 3800, Australia
Ph.: +61 3 9905 8346 (W), +61 3 9543 1958 (R)
Web: http://www.buseco.monash.edu.au/staff/profile.php?uid=rahmed
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