unique(): Using unique() and nunique() in Pandas DataFrames

Parameters

Examples with Parameters

import pandas as pd 
my_dict={'NAME':['Ravi','Raju','Alex','Ron','King','Jack'],
         'ID':[1,2,3,4,5,6],
         'GAME':['CRICKET','TENNIS','CRICKET','HOCKEY','CRICKET','TENNIS'],
         'CLASS1':['Four','Three','Three','Four','Five','Three']}
my_data = pd.DataFrame(data=my_dict)
print(my_data['CLASS1'].unique())

['Four' 'Three' 'Five']

print(my_data['GAME'].unique())

['CRICKET' 'TENNIS' 'HOCKEY']

print(my_data['CLASS1'].nunique())

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Example: Finding Unique Values Across Multiple Columns

We can use `unique()` to get distinct values across different columns. This is helpful when analyzing multiple categories.

import pandas as pd
my_data = pd.DataFrame({
    'A': [1, 2, 2, 3, 4],
    'B': [4, 4, 3, 3, 2]
})
unique_values = pd.concat([my_data['A'], my_data['B']]).unique()
print(unique_values)  

[1 2 3 4]  

Use Case: Comparing Unique Values in Different DataFrames

When working with multiple datasets, you may want to compare unique values to identify overlaps or discrepancies.

import pandas as pd
  df1 = pd.DataFrame({'City': ['NY', 'LA', 'SF', 'NY']})
df2 = pd.DataFrame({'City': ['NY', 'DC', 'SF', 'Chicago']})

unique_cities_df1 = df1['City'].unique()
unique_cities_df2 = df2['City'].unique()

common_cities = set(unique_cities_df1).intersection(unique_cities_df2)
print(common_cities)

{'NY', 'SF'}

Advanced Feature: Using `unique()` with Categorical Data

Pandas can work more efficiently by converting columns to categorical types before using `unique()`, especially with repeated data.

my_data['Category'] = my_data['A'].astype('category')
unique_categories = my_data['Category'].unique()
print(unique_categories)

Example: Counting Unique Values Using `nunique()`

Alongside `unique()`, we can use `nunique()` to quickly count distinct entries in a column.

import pandas as pd
  data = pd.Series(['apple', 'orange', 'apple', 'banana', 'orange'])
unique_count = data.nunique()
print(unique_count)

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Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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