Comparing two Pandas series and printing the the difference

In this article, we will compare two Pandas series and print the differences between them. By difference, we mean the index positions where elements did not match, along with the actual values from both series.

What is Series Comparison?

Pandas provides the compare() method to identify differences between two series. This method returns a DataFrame showing only the positions where values differ, with columns representing each series.

Basic Example

Let's start with a simple comparison between two series ?

import pandas as pd

s1 = pd.Series([10, 20, 30, 40, 50, 60])
s2 = pd.Series([10, 30, 30, 40, 55, 60])

print("S1:")
print(s1)
print("\nS2:")
print(s2)

difference = s1.compare(s2)
print("\nDifference between the series:")
print(difference)

S1:
0    10
1    20
2    30
3    40
4    50
5    60
dtype: int64

S2:
0    10
1    30
2    30
3    40
4    55
5    60
dtype: int64

Difference between the series:
   self  other
1  20.0   30.0
4  50.0   55.0

Understanding the Output

The comparison output shows a DataFrame with two columns:

• self − Values from the first series (s1)
• other − Values from the second series (s2)

Only rows where values differ are displayed. In our example, differences occur at index 1 (20 vs 30) and index 4 (50 vs 55).

Comparing Series with Different Lengths

When series have different lengths, compare() handles missing values gracefully ?

import pandas as pd

s1 = pd.Series([1, 2, 3, 4])
s2 = pd.Series([1, 2, 5])

difference = s1.compare(s2)
print("Difference between series of different lengths:")
print(difference)

Difference between series of different lengths:
   self  other
2   3.0    5.0
3   4.0    NaN

Using keep_equal Parameter

To see both matching and differing values, use keep_equal=True ?

import pandas as pd

s1 = pd.Series([10, 20, 30])
s2 = pd.Series([10, 25, 30])

difference = s1.compare(s2, keep_equal=True)
print("Comparison with equal values shown:")
print(difference)

Comparison with equal values shown:
   self  other
0  10.0   10.0
1  20.0   25.0
2  30.0   30.0

Conclusion

The compare() method is an efficient way to identify differences between two Pandas series. It returns a DataFrame showing only differing positions by default, with options to include equal values when needed.