       Drop the columns where at least one element is missing.

        >>> df.dropna(axis='columns')
               name
        0    Alfred
        1    Batman
        2  Catwoman

        Drop the rows where all elements are missing.

        >>> df.dropna(how='all')
               name        toy       born
        0    Alfred        NaN        NaT
        1    Batman  Batmobile 1940-04-25
        2  Catwoman   Bullwhip        NaT

        Keep only the rows with at least 2 non-NA values.

        >>> df.dropna(thresh=2)
               name        toy       born
        1    Batman  Batmobile 1940-04-25
        2  Catwoman   Bullwhip        NaT

        Define in which columns to look for missing values.

        >>> df.dropna(subset=['name', 'toy'])
               name        toy       born
        1    Batman  Batmobile 1940-04-25
        2  Catwoman   Bullwhip        NaT
        zBYou cannot set both the how and thresh arguments at the same time.rő