Using std.algorithm how to uniq and sort a multidimensional array?

[Gary Willoughby]

Using std.algorithm how to uniq and sort a multidimensional array?

e.g. the uniq function takes a function as a predicate but i'm 
confused how to handle the multiple dimensions.

     string[][] tags;

     tags = tags.uniq!("a[0][1] == b[1][1]").array;

The above is my attempt and it failed.