.loc is an indexer. It looks for an entry in the index, but the column name is not an index. It is simply a column. The following solutions would work:

df.loc[4, 'rating'] = 100 # Because 4 is in the index, but how do you know?

or:

df.loc[df['name']=='cheerio', 'rating'] = 100 # Find the row by column

or:

df.set_index('name', inplace=True) # Make 'name' the index
df.loc['cheerios', 'rating'] = 100     # Use the indexer
Answer from DYZ on Stack Overflow
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Pandas
pandas.pydata.org โ€บ docs โ€บ reference โ€บ api โ€บ pandas.DataFrame.replace.html
pandas.DataFrame.replace โ€” pandas 3.0.6 documentation
Replace values given in to_replace with value. Values of the Series/DataFrame are replaced with other values dynamically.
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Python Course
python-course.eu โ€บ numerical-programming โ€บ accessing-and-changing-values-dataframes.php
27. Accessing and Changing values of DataFrames | python-course.eu
So we have to change our DataFrame accodingly: df.replace("programmer", "computer scientist", inplace=True) df ยท to_replace can be a list consisting of str, regex or numeric objects. If both the values of to_replace and value are both lists, they must be the same length.
Discussions

python - Trying to change a single value in pandas dataframe - Stack Overflow
I've seen a bunch of questions with similar titles but I still cant figure it out. All I want to do is replace the value thats in my dataframe in the fifth row and 5th column with the value 100. I More on stackoverflow.com
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python - Replace single value in a pandas dataframe, when index is not known and values in column are unique - Stack Overflow
There is a question on SO with the title "Set value for particular cell in pandas DataFrame", but it assumes the row index is known. How do I change a value, if the row values in the relevant colum... More on stackoverflow.com
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June 20, 2018
python - How do i replace the value of a data-frame column with a single value? - Stack Overflow
0 How to find and replace a single value in a dataframe in python More on stackoverflow.com
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Pandas: Need to replace only a certain value with another value from a different dataframe.
df = pd.merge(df1, df2, left_on='Project Name', right_on='Name of Project', how='left') cond = df['Project Owner'] == 'Default' df.loc[cond, 'Project Owner'] = df.loc[cond, 'Owner of Project'] There's probably an easier solution, but I can't think of it. Edit: Actually there is something a little easier. Instead of using the condition and loc, you can use combine_first to combine the non NA values between the two columns df = pd.merge(df1, df2, left_on='Project Name', right_on='Name of Project', how='left') df['Project Owner'] = df['Project Owner'].combine_first(df['Owner of Project']) Use this if you want to drop the two new columns. df = df.drop(columns=['Name of Project', 'Owner of Project']) More on reddit.com
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Statology
statology.org โ€บ home โ€บ how to replace values in a pandas dataframe (with examples)
How to Replace Values in a Pandas DataFrame (With Examples)
September 27, 2022 - The following code shows how to replace multiple values in an entire pandas DataFrame: #replace 'E' with 'East' and 'W' with 'West' df = df.replace(['E', 'W'],['East', 'West']) #view DataFrame print(df) team division rebounds 0 A East 11 1 A West 8 2 B East 7 3 B East 6 4 B West 6 5 C West 5 6 C East 12 ยท The following code shows how to replace a single value in a single column:
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Vultr Docs
docs.vultr.com โ€บ python โ€บ third party โ€บ pandas โ€บ dataframe โ€บ replace()
Python Pandas DataFrame replace() - Replace Values
December 27, 2024 - Prepare a DataFrame with several integers. Use replace() to swap a list of values with another list. ... Here, 1 is replaced by 11 and 3 by 33 across the entire DataFrame.
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Medium
medium.com โ€บ @punya8147_26846 โ€บ replace-values-in-pandas-dataframe-9299986d47c3
Replace values in Pandas DataFrame | by Punyakeerthi BL | Medium
June 24, 2024 - It offers a flexible approach to substituting specific values, patterns, or ranges with alternative values. dataframe.replace(to_replace, value, inplace=False, limit=None, regex=False) to_replace: This parameter specifies the value(s) or pattern(s) ...
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Note.nkmk.me
note.nkmk.me โ€บ home โ€บ python โ€บ pandas
pandas: Replace values in DataFrame and Series with replace() | note.nkmk.me
January 17, 2024 - In pandas, the replace() method allows you to replace values in DataFrame and Series. It is also possible to replace parts of strings using regular expressions (regex). pandas.DataFrame.replace โ€” pan ...
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datagy
datagy.io โ€บ home โ€บ pandas tutorials โ€บ pandas dataframes โ€บ pandas replace() โ€“ replace values in pandas dataframe
Pandas replace() - Replace Values in Pandas Dataframe โ€ข datagy
March 2, 2023 - The Pandas DataFrame.replace() method can be used to replace a string, values, and even regular expressions (regex) in your DataFrame. The entire post has been rewritten in order to make the content clearer and easier to follow.
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PythonForBeginners.com
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Pandas Replace Value in a Dataframe - PythonForBeginners.com
January 4, 2023 - Then, we invoked the replace() ... of 100 with "Max" and returns a new series. To replace a value in a pandas dataframe, We will invoke the replace() method on the dataframe....
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GeeksforGeeks
geeksforgeeks.org โ€บ data analysis โ€บ python-pandas-dataframe-replace
Python | Pandas dataframe.replace() - GeeksforGeeks
Pandas dataframe.replace() function is used to replace a string, regex, list, dictionary, series, number, etc. from a Pandas Dataframe in Python. Every instance of the provided value is replaced after a thorough search of the full DataFrame.
Published: July 11, 2025
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Reddit
reddit.com โ€บ r/learnpython โ€บ pandas: need to replace only a certain value with another value from a different dataframe.
r/learnpython on Reddit: Pandas: Need to replace only a certain value with another value from a different dataframe.
January 31, 2024 -

I'm losing my mind on this one. I have two dataframes. For simplicity's sake, in df1, let's say there's a column with a project name, and a column with the project owner. Due to a change in systems, some project owners have been replaced with "Default." In df2, I have all the projects and project owners, but only for the "Default" folk. There are, of course, many other columns on both dataframes, but I'm omitting them. Also, the dataframes have completely different column names. I only mention because it's one of the errors I've run into. This is for a script I run every week for work that needs to be changed due to the aforementioned new system.

Example of df1:

Project Name Project Owner
Project A Bob Jones
Project B Default
Project C Default
Project D John Roberts

Example of df2:

Name of Project Owner of Project
Project B Bertha Thomas
Project C Jane Smith

I've tried:

project_dict = dict(zip(df2['Name of Project'], df2['Owner of Project']))
df['Project Owner'] = df['Project Name'].replace(project_dict)

Which outputs:

Project Name Project Owner
Project A Project A
Project B Bertha Thomas
Project C Jane Smith
Project D Project D

I've also tried every way to use loc I could think of, and I'm just lost. The above is the closest I've gotten. Any ideas would be appreciated, and don't hesitate to let me know if I need to post more code.

Thanks!

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Saturn Cloud
saturncloud.io โ€บ blog โ€บ how-to-replace-values-on-specific-columns-in-pandas
How to Replace Values on Specific Columns in Pandas | Saturn Cloud Blog
May 1, 2026 - This code snippet will replace all occurrences of New York in the City column with NY. Setting inplace=True modifies the original DataFrame; otherwise, it returns a new DataFrame with the replacements. You can use .loc[] to replace values based on a condition.
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Favtutor
favtutor.com โ€บ articles โ€บ pandas-replace-column-values
Pandas DataFrame: Replace Column Values (with code)
December 15, 2023 - Here are 4 unique ways to replace column values in Pandas DataFrame: The Pandas library provides the .replace() method in Python to replace columns in a DataFrame. The .replace() method is a versatile way to replace values in a Pandas DataFrame.
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Stack Overflow
stackoverflow.com โ€บ questions โ€บ 70396881 โ€บ how-to-replace-single-value-in-pandas-dataframe-by-index
python - How to replace single value in pandas dataframe by index - Stack Overflow
df_a = pd.DataFrame(data={"a": [0, 0, 0], "b": [0, 0, 0]}) df_a.at[2, "b"] = 10 display(df_a) a b 0 0 0 1 0 0 2 10 0 ยท NOTE: python df_a.iat[2,1] can be used to achieve the same result if wanting to use integer-based column indexes.
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Saturn Cloud
saturncloud.io โ€บ blog โ€บ how-to-replace-column-values-in-a-pandas-dataframe
How to Replace Column Values in a Pandas DataFrame | Saturn Cloud Blog
May 1, 2026 - In this example, we created a DataFrame with two columns (โ€˜Aโ€™ and โ€˜Bโ€™). We then used the .replace() method to replace the value โ€˜fooโ€™ in column โ€˜Aโ€™ with the value โ€˜quxโ€™. The inplace=True parameter tells Pandas to modify the ...