Counting and retrieving Unique elements from a pandas.Series object

Overview:

The count() function returns the number of elements present in a pandas.Series instance.The NA/null/None values are not included in the count value.
The nunique() function returns the number of unique elements present in the pandas.Series.
The function Series.unique() returns the unique elements excluding the duplicate values present in a pandas.Series. Determining uniqueness of the elements is done through a hash table.

Example - Counting elements of a pandas.series:

# Example Python program to count the number of

# elements present in a pandas.Series instance

import pandas as pds

cities = ["London", "Paris", "Madrid", "NewYork", "Chicago", "San Francisco"];

# Create a pandas.Series instance

series = pds.Series(cities);

print("Contents of the pandas.series:");

print(cities);

print("Number of elements present in the pandas.series:");

print(series.count());

Output:

Contents of the pandas.series:

['London', 'Paris', 'Madrid', 'NewYork', 'Chicago', 'San Francisco']

Number of elements present in the pandas.series:

Example-Count and get the unique elements present in a pandas.series:

# Example Python program to get unique elements present in a pandas.Series

import pandas as pds

# Create a pandas.Series instance

numbers = pds.Series([1,2,3,5,7,3,5,7,3,5,7]);

print("Contents of the Series:");

print(numbers);

print("Number of Unique elements present in the Series:");

print(numbers.nunique());

print("Unique elements of the Series:");

print(numbers.unique());

Output:

Contents of the Series:

0 1

1 2

2 3

3 5

4 7

5 3

6 5

7 7

8 3

9 5

10 7

dtype: int64

Number of Unique elements present in the Series:

Unique elements of the Series:

[1 2 3 5 7]

Example- Get the unique class objects present in a pandas.series:

# Example Python program to get unique elements present in a pandas.Series

import pandas as pds

class X:

def __init__(self, name):

self.name = name;

def __str__(self):

return self.name;

# Unique elements

x1 = X("x1");

x2 = X("x2");

x3 = X("x3");

# Copy

x4 = x1;

# Copy is not returned as identity of x1 and x4 are same

xSeries = pds.Series([x1, x2, x3, x4]);

uniques = xSeries.unique();

print("Unique objects:");

print(uniques);

# First and fourth elements have indeed different identities

xDashSeries = pds.Series([X("One"), X("Two"), X("Three"), X("One")]);

uniques = xDashSeries.unique();

print("Unique objects:")

print(uniques);

Output:

Unique objects:

[<__main__.X object at 0x1100db438> <__main__.X object at 0x1100db470>

<__main__.X object at 0x1100db4a8>]

Unique objects:

[<__main__.X object at 0x11c0a8da0> <__main__.X object at 0x11d4fe0b8>

<__main__.X object at 0x11d4fe048> <__main__.X object at 0x11d52a940>]