Off topic:Find uniqueness in rows with NA?

Question

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I have a data like below. I would like to find unique rows (uniqueness). But in this file I have 'NA' that I like if all value in row with NA value is same with other rows (like rows: 1,2,5) I want to ignore it, but if not same (like rows : 2,4 0r 2,5) I like to keep it as unique row.

data:

    [,1] [,2] [,3] [,4]
c1    2    1    3   NA
c2    2    1    3    3
c3    2    1    4    3
c4    2    2    3   NA
c5    2    1    3    3
c6    2    NA   3   NA

I would like to have this output:

output:

c2    2    1    3    3
c3    2    1    4    3
c4    2    2    3   NA

Thanks for your help in advance.