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pandas: Handle strings (replace, strip, case conversion, etc.)

Posted: | Tags: Python, pandas

You can use various methods with the string accessor (str.xxx()) to handle (replace, strip, etc.) strings of pandas.Series (= a column or row of pandas.DataFrame).

For example, the following methods are available. You can apply the same methods for standard Python strings (str) to all elements of pandas.Series.

  • Replace each string in pandas.Series
    • str.replace()
  • Strip each string in pandas.Series
    • str.strip()
    • str.lstrip()
    • str.rstrip()
  • Convert the case of each string in pandas.Series
    • str.lower()
    • str.upper()
    • str.capitalize()
    • str.title()

See also the following articles for other string methods.

Replace each string in pandas.Series

str.replace()

import pandas as pd

s = pd.Series([' a-a-x ', ' b-x-b ', ' x-c-c '])
print(s)
# 0     a-a-x 
# 1     b-x-b 
# 2     x-c-c 
# dtype: object

s_new = s.str.replace('x', 'z')
print(s_new)
# 0     a-a-z 
# 1     b-z-b 
# 2     z-c-c 
# dtype: object
source: pandas_str_replace_strip_etc.py

To update a column in pandas.DataFrame, assign the new column to the original column. The same applies to other methods.

df = pd.DataFrame([[' a-a-x-1 ', ' a-a-x-2 '],
                   [' b-x-b-1 ', ' b-x-b-2 '],
                   [' x-c-c-1 ', ' x-c-c-2 ']],
                  columns=['col1', 'col2'])
print(df)
#         col1       col2
# 0   a-a-x-1    a-a-x-2 
# 1   b-x-b-1    b-x-b-2 
# 2   x-c-c-1    x-c-c-2 

df['col1'] = df['col1'].str.replace('x', 'z')
print(df)
#         col1       col2
# 0   a-a-z-1    a-a-x-2 
# 1   b-z-b-1    b-x-b-2 
# 2   z-c-c-1    x-c-c-2
source: pandas_str_replace_strip_etc.py

If you want to replace not a substring but the element itself, use the replace() method of pandas.DataFrame or pandas.Series.

Strip each string in pandas.Series

str.strip()

By default, whitespace characters at the left and right ends (= leading and trailing whitespace characters) are removed.

s_new = s.str.strip()
print(s_new)
# 0    a-a-x
# 1    b-x-b
# 2    x-c-c
# dtype: object
source: pandas_str_replace_strip_etc.py

You can specify characters to be removed. Characters in the specified string are removed. The same applies to str.lstrip() and str.rstrip().

s_new = s.str.strip(' x')
print(s_new)
# 0     a-a-
# 1    b-x-b
# 2     -c-c
# dtype: object
source: pandas_str_replace_strip_etc.py

For pandas.DataFrame:

df['col1'] = df['col1'].str.strip()
print(df)
#       col1       col2
# 0  a-a-z-1   a-a-x-2 
# 1  b-z-b-1   b-x-b-2 
# 2  z-c-c-1   x-c-c-2
source: pandas_str_replace_strip_etc.py

str.lstrip()

str.lstrip() strips only the characters on the left side.

s_new = s.str.lstrip()
print(s_new)
# 0    a-a-x 
# 1    b-x-b 
# 2    x-c-c 
# dtype: object
source: pandas_str_replace_strip_etc.py

str.rstrip()

str.rstrip() strips only the characters on the right side.

s_new = s.str.rstrip()
print(s_new)
# 0     a-a-x
# 1     b-x-b
# 2     x-c-c
# dtype: object
source: pandas_str_replace_strip_etc.py

Convert the case of each string in pandas.Series

The following pandas.DataFrame is used as an example.

s = pd.Series(['Hello World', 'hello world', 'HELLO WORLD'])
print(s)
# 0    Hello World
# 1    hello world
# 2    HELLO WORLD
# dtype: object
source: pandas_str_replace_strip_etc.py

str.lower()

s_new = s.str.lower()
print(s_new)
# 0    hello world
# 1    hello world
# 2    hello world
# dtype: object
source: pandas_str_replace_strip_etc.py

str.upper()

s_new = s.str.upper()
print(s_new)
# 0    HELLO WORLD
# 1    HELLO WORLD
# 2    HELLO WORLD
# dtype: object
source: pandas_str_replace_strip_etc.py

str.capitalize()

s_new = s.str.capitalize()
print(s_new)
# 0    Hello world
# 1    Hello world
# 2    Hello world
# dtype: object
source: pandas_str_replace_strip_etc.py

str.title()

s_new = s.str.title()
print(s_new)
# 0    Hello World
# 1    Hello World
# 2    Hello World
# dtype: object
source: pandas_str_replace_strip_etc.py

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