blz blz - 1 month ago 17
Python Question

How can I obtain the element-wise logical NOT of a pandas Series?

I have a relatively straightforward question, today. I have a pandas

Series
object containing boolean values. How can I get a series containing the logical
NOT
of each value?

For example, consider a series containing:

True
True
True
False


The series I'd like to get would contain:

False
False
False
True


This seems like it should be reasonably simple, but apparently I've misplaced my mojo today =(

Thanks!

Answer

To invert a boolean Series, use ~s:

In [7]: s = pd.Series([True, True, False, True])

In [8]: ~s
Out[8]: 
0    False
1    False
2     True
3    False
dtype: bool

Using Python2.7, NumPy 1.8.0, Pandas 0.13.1:

In [119]: s = pd.Series([True, True, False, True]*10000)

In [10]:  %timeit np.invert(s)
10000 loops, best of 3: 91.8 µs per loop

In [11]: %timeit ~s
10000 loops, best of 3: 73.5 µs per loop

In [12]: %timeit (-s)
10000 loops, best of 3: 73.5 µs per loop

As of Pandas 0.13.0, Series are no longer subclasses of numpy.ndarray; they are now subclasses of pd.NDFrame. This might have something to do with why np.invert(s) is no longer as fast as ~s or -s.

Caveat: timeit results may vary depending on many factors including hardware, compiler, OS, Python, NumPy and Pandas versions.