Function of pandas DataFrame that creates single value output

Question

I have a DataFrame made of boolean values. What I want is to check whether all entries are True by applying some function that simply outputs True or False after looking at each individual entry. Is there an easy or elegant way to do this?

And more generally speaking, say I have some DataFrame and I want to apply a function to the entries and output a single value (eg sum all the elements up, or take the product of all the elements).Is there some native way to create a function of the form

def f(df):
   return single_value(df)

I have seen plenty of methods that subject DataFrame entries to functions, but they all return a DataFrame (most of the time changing it in place). A mathematical example of what I want would be a vector norm since it maps vectors (series in pds) to positive real values.

Answer 1

If you want to check whether the entire dataframe contains only True boolean values then all you need is

df.eq(True).all()

and the output will be a Series that indicates whether each column has True values. For instance,

>>> import pandas as pd 
>>> df = pd.DataFrame({'col1': [True, True], 'col2': [True, False], 'col3': [True, None]})
>>> df.eq(True).all()
col1     True
col2    False
col3    False
dtype: bool

Now if you want the output to be a single boolean value then you can apply all() on the above:

>>> df.eq(True).all().all()
False

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• eq() can be used to perform element-wise comparisons
• all() is used to check whether all elements are True , potentially over an axis.