python - How to implement a Boolean search with multiple columns in pandas

Question

I have a pandas df and would like to accomplish something along these lines (in SQL terms):

SELECT * FROM df WHERE column1 = 'a' OR column2 = 'b' OR column3 = 'c' etc.

Now this works, for one column/value pair:

foo = df.loc[df['column']==value]

However, I'm not sure how to expand that to multiple column/value pairs.

• To be clear, each column matches a different value.

Answer 1

You need to enclose multiple conditions in braces due to operator precedence and use the bitwise and (&) and or (|) operators:

foo = df[(df['column1']==value) | (df['columns2'] == 'b') | (df['column3'] == 'c')]

If you use and or or, then pandas is likely to moan that the comparison is ambiguous. In that case, it is unclear whether we are comparing every value in a series in the condition, and what does it mean if only 1 or all but 1 match the condition. That is why you should use the bitwise operators or the numpy np.all or np.any to specify the matching criteria.

There is also the query method: http://pandas.pydata.org/pandas-docs/dev/generated/pandas.DataFrame.query.html

but there are some limitations mainly to do with issues where there could be ambiguity between column names and index values.