ENH: add DataFrame.is_unique method
Currently, to see columns with unique values, we have to do `df.apply(lambda x: x.is_unique)`, which is a bit awkward.

IMO checking for unique columns in a DataFrame is a common enough need to justify a method for that specific purpose.

Xref: #11948
For a DataFrame, `is_unique` could also be interpreted as whether the DataFrame has all unique rows? @jorisvandenbossche that's true, and could be fixes by having an `axis` parameter. I didn't ínclude it, because `duplicated` doesn't have one and worried that doing `self.T.is_unique()` would change the types for the values and could give wrong results. Not sure about that one, actually. This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. @topper-123 this was close, can you merge master and move the note to 1.3 Ok, done. Looks pretty good overall. Should there be a corresponding `Series.is_unique` method as well? There is a `Series.duplicated` method (as your referenced `duplicated` earlier) Thanks for the PR, but it appears that it's gone stale. Please let us know if you'd like to continue by merging master and targeting for 1.4.