Pandas: Filter By Values Within Multiple Columns

I'm trying to filter a dataframe based on the values within the multiple columns, based on a single condition, but keep other columns to which I don't want to apply the filter at a

Solution 1:

You first want to substitute your 'NONE' with np.nan so that it is recognized as a null value by dropna. Then use loc with your boolean series and column subset. Then use dropna with axis=1 and how='all'

df.replace('NONE', np.nan) \
    .loc[df.month == df.month.max(), l].dropna(axis=1, how='all')

   month     a
3      2     A
4      2  NONE