Pandas Replace Substring in DataFrame

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  • Post category:Pandas
  • Post last modified:May 16, 2024
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You can find out how to replace substring in a column of Pandas DataFrame using DataFrame.replace() with lambda functions. In this article, I will explain how to replace the substring in the DataFrame column with multiple examples.

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Key Points –

  • Replace a substring with another substring in Pandas.
  • Replace a pattern of a substring with another substring using regular expression.
  • Specify the column containing the target substrings within the DataFrame.
  • Use the str.replace() method in Pandas to replace substrings within DataFrame columns.
  • Provide the substring to be replaced and the replacement string as arguments to the str.replace() method.

Related: You can replace the string in Pandas DataFrame.

Quick Examples to Replace Substring

Below are quick examples of replace a substring in a column of pandas DataFrame.


# Quick examples to replace substring

# Example 1: Replace substring
df2 = df.replace('Py','Python with ', regex=True)

# Example 2: Replace substring
df2 = df.replace('Py','Python with ', regex=True)

# Example 3: Replace multiple substrings
df2 = df.replace({'Courses': 'Py', 'Duration': 'days'}, 
    {'Courses': 'Python with', 'Duration': ' Days'}, regex=True)

# Example 4: Replace pattern of Substring 
# Using regular expression.
df2=df.replace(regex=['Language'],value='Lang')

# Example 5: Using str.replace()
df['Courses'] = df['Courses'].str.replace('Language','Lang')

# Example 6: Replace SubString 
# Using apply() function with lambda
df2 = df.apply(lambda x: x.replace(
    {'Py':'Python with', 'Language':'Lang'},
    regex=True))

To run some examples of replace substring in Pandas DataFrame, let’s create Pandas DataFrame using data from a dictionary.


# Create a pandas DataFrame.
import pandas as pd
import numpy as np
technologies= {
    'Courses':["Spark","PySpark","Spark","Java Language","PySpark","PHP Language"],
    'Fee' :[22000,25000,23000,24000,26000,27000],
    'Duration':['30days','50days','30days','60days','35days','30days']
          }
df = pd.DataFrame(technologies)
print("Create DataFrame:\n", df)

Yields below output.

pandas replace substring

Replace Substring Using replace()

To replace substrings in a DataFrame using the DataFrame.replace() function. This function by default finds the exact string match and replaces it with the specified value. Use regex=True to replace the substring.


# Replace substring
df2 = df.replace('Py','Python with ', regex=True)
print("After replacing the substring with another substring:\n", df2)

# Replacing substring 'Py' with 'Python with' using replace() function
df['Courses'] = df['Courses'].replace('Py', 'Python with ', regex=True)
print("After replacing the substring with another substring:\n", df)

Yields below output. The above example replaced the substring value Py with Python on column Courses.

pandas replace substring

This method returns a new DataFrame after replacing the substring. Use inplace=True to replace on existing DataFrame object.

Replace Multiple Substrings

Alternatively, you can apply this method to multiple string columns in a DataFrame and allows you to replace occurrences of substrings with other substrings. Let’s see how to replace substring on multiple columns, to do this I will be using dict with column names and values to replace.


# Replace multiple substrings
df2 = df.replace({'Courses': 'Py', 'Duration': 'days'}, 
    {'Courses': 'Python with', 'Duration': ' Days'}, regex=True)
print("After replacing the multiple substrings:\n", df2)

Yields below output. 


# Output:
# After replacing the multiple substrings:
            Courses    Fee Duration
0             Spark  22000  30 Days
1  Python withSpark  25000  50 Days
2             Spark  23000  30 Days
3     Java Language  24000  60 Days
4  Python withSpark  26000  35 Days
5      PHP Language  27000  30 Days

Replace Pattern of Substring

To replace a pattern of substring using regular expression in Python, you can utilize the str.replace() method with the regex=True parameter in pandas. 


# Replace pattern of Substring using regular expression.
df2=df.replace(regex=['Language'],value='Lang')
print("After replacing the substring:\n", df2)

This code will replace the substring Language with Lang in the Courses column of the DataFrame using regular expressions. The regex=True parameter enables regular expression matching in the replace() method. 


# Output:
# After replacing the substring:
     Courses    Fee Duration
0      Spark  22000   30days
1    PySpark  25000   50days
2      Spark  23000   30days
3  Java Lang  24000   60days
4    PySpark  26000   35days
5   PHP Lang  27000   30days

Using str.replace() Function

Alternatively, when replacing a substring in a DataFrame column, you can utilize the str.replace() method. By default, replace() seeks exact matches unless you provide a regex pattern and set the parameter regex=True.


# By using str.replace()
df['Courses'] = df['Courses'].str.replace('Language','Lang')
print("After replacing the substring:\n", df)

In this program, df['Courses'].str.replace('Language','Lang') directly replaces the substring Language with Lang in the Courses column using the str.replace() method on the DataFrame. Note that this replaces the value on the Courses column in the existing DataFrame object. This example yields the below output.


# Output:
# After replacing the substring:
     Courses    Fee Duration
0      Spark  22000   30days
1    PySpark  25000   50days
2      Spark  23000   30days
3  Java Lang  24000   60days
4    PySpark  26000   35days
5   PHP Lang  27000   30days

Replace Substring Using apply() Function with Lambda

In this section, You can find out how to replace the substring using DataFrame.apply() and lambda function. The apply() function in Pandas enables you to apply a function along one of the axes of the DataFrame, be it rows or columns.. The below example replaces multiple substring’s.


# Replace SubString using apply() function with lambda.
df2 = df.apply(lambda x: x.replace({'Py':'Python with', 'Language':'Lang'}, regex=True))
print(df2)

Yields below output.


# Output:
            Courses    Fee Duration
0             Spark  22000   30days
1  Python withSpark  25000   50days
2             Spark  23000   30days
3         Java Lang  24000   60days
4  Python withSpark  26000   35days
5          PHP Lang  27000   30days

Complete Example of Pandas Replace Substring


# Create a pandas DataFrame.
import pandas as pd
import numpy as np
technologies= {
    'Courses':["Spark","PySpark","Spark","Java Language","PySpark","PHP Language"],
    'Fee' :[22000,25000,23000,24000,26000,27000],
    'Duration':['30days','50days','30days','60days','35days','30days']
          }
df = pd.DataFrame(technologies)
print(df)

# Replace substring
df2 = df.replace('Py','Python with ', regex=True)
print(df2)

# Replace substring
df2 = df.replace('Py','Python with ', regex=True)
print(df2)

# Replace multiple substrings
df2 = df.replace({'Courses': 'Py', 'Duration': 'days'}, 
    {'Courses': 'Python with', 'Duration': ' Days'}, regex=True)
print(df2)

# Replace pattern of Substring using regular expression.
df2=df.replace(regex=['Language'],value='Lang')
print(df2)

# Using str.replace()
df['Courses'] = df['Courses'].str.replace('Language','Lang')
print(df)

# Replace SubString using apply() function with lambda.
df2 = df.apply(lambda x: x.replace(
    {'Py':'Python with', 'Language':'Lang'},
    regex=True))
print(df2)

FAQ on Replace Substring

How can I replace a substring in a column of a Pandas DataFrame?

You can replace a substring in a column of a DataFrame using various methods such as str.replace(), apply() with a lambda function, or replace() method.

How can I replace substrings conditionally based on their values?

You can replace substrings conditionally based on their values using pandas’ str.replace() method along with conditional statements.

What is the difference between str.replace() and replace() method?

The str.replace() method is used specifically for string columns and replaces substrings within each string element of the column. On the other hand, the replace() method is more general and can be used to replace values in any type of column, not just strings.

Can I replace a substring using regular expressions in Pandas?

You can replace substrings using regular expressions in Pandas by setting the regex parameter to True in the str.replace() method or providing a regex pattern in the replace() method.

How can I replace substrings efficiently in a large DataFrame?

To replace substrings efficiently in a large DataFrame, it’s recommended to use vectorized operations such as str.replace() or replace() method with regex pattern if needed, as they are optimized for performance.

Conclusion

In conclusion, replacing substrings within a Pandas DataFrame is a common operation in data preprocessing and cleaning tasks. Throughout this article, we have explored various methods and techniques to accomplish this, focusing on the replace() method along with lambda functions for flexibility and customization.

References

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