How do you change a column value in python?

Depending on your needs, you may use either of the following approaches to replace values in Pandas DataFrame:

(1) Replace a single value with a new value for an individual DataFrame column:

df['column name'] = df['column name'].replace(['old value'],'new value')

(2) Replace multiple values with a new value for an individual DataFrame column:

df['column name'] = df['column name'].replace(['1st old value','2nd old value',...],'new value')

(3) Replace multiple values with multiple new values for an individual DataFrame column:

df['column name'] = df['column name'].replace(['1st old value','2nd old value',...],['1st new value','2nd new value',...])

(4) Replace a single value with a new value for an entire DataFrame:

df = df.replace(['old value'],'new value')

In the next section, you’ll see how to apply the above templates in practice.

Step 1: Gather your Data

To begin, gather your data with the values that you’d like to replace.

For example, let’s gather the following data about different colors:

You’ll later see how to replace some of the colors in the above table.

Step 2: Create the DataFrame

Next, create the DataFrame based on the data that was captured in step 1:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])

print (df)

Run the code in Python, and you’ll see the following DataFrame:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3      Blue       White
4      Blue       White
5       Red        Blue
6       Red        Blue
7       Red        Blue

Step 3: Replace Values in Pandas DataFrame

Let’s now replace all the ‘Blue’ values with the ‘Green’ values under the ‘first_set’ column.

You may then use the following template to accomplish this goal:

df['column name'] = df['column name'].replace(['old value'],'new value')

And this is the complete Python code for our example:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])
df['first_set'] = df['first_set'].replace(['Blue'],'Green')

print (df)

Run the code, and you’ll notice that all the ‘Blue’ values got replaced with the ‘Green’ values under the first column:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3     Green       White
4     Green       White
5       Red        Blue
6       Red        Blue
7       Red        Blue

But what if you want to replace multiple values with a new value for an individual DataFrame column?

If that’s the case, you may use this template:

df['column name'] = df['column name'].replace(['1st old value','2nd old value',...],'new value')

Let’s say that you’d like to replace the ‘Blue’ and ‘Red’ colors with a ‘Green’ color under the ‘first_set’ column.

This is the syntax that you may use in Python:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])
df['first_set'] = df['first_set'].replace(['Blue','Red'],'Green')

print (df)

You’ll now notice that both the ‘Blue’ and ‘Red’ colors got replaced with a ‘Green’ color under the first column:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3     Green       White
4     Green       White
5     Green        Blue
6     Green        Blue
7     Green        Blue

Suppose that you want to replace multiple values with multiple new values for an individual DataFrame column.

In that case, you may use this template:

df['column name'] = df['column name'].replace(['1st old value','2nd old  value',...],['1st new value','2nd new value',...])

Let’s say that you want to replace:

• The ‘Blue’ color with a ‘Green’ color; and
• The ‘Red’ color with a ‘White’ color

You can then apply this code in Python:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])
df['first_set'] = df['first_set'].replace(['Blue','Red'],['Green','White'])

print (df)

You’ll notice that the ‘Blue’ became ‘Green’ and the ‘Red’ became ‘White’ under the first column:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3     Green       White
4     Green       White
5     White        Blue
6     White        Blue
7     White        Blue

So far you have seen how to replace values under an individual DataFrame column.

But what if you’d like to replace a value across the entire DataFrame?

In that case, you may use the following template:

df = df.replace(['old value'],'new value')

For example, you may run the code below in order to replace the ‘Blue’ color with a ‘Green’ color throughout the entire DataFrame:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])
df = df.replace(['Blue'],'Green')

print (df)

Once you run the code, you’ll see that ‘Blue’ became ‘Green’ across all the columns in the DataFrame:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3     Green       White
4     Green       White
5       Red       Green
6       Red       Green
7       Red       Green

And if you decide, for example, to replace two colors, such as ‘Blue’ and ‘Red’ into ‘Green,’ then you may use this syntax:

import pandas as pd

colors = {'first_set':  ['Green','Green','Green','Blue','Blue','Red','Red','Red'],
          'second_set': ['Yellow','Yellow','Yellow','White','White','Blue','Blue','Blue']
         }

df = pd.DataFrame(colors, columns= ['first_set','second_set'])
df = df.replace(['Blue','Red'],'Green')

print (df)

Both the ‘Blue’ and ‘Red’ colors would be replaced with ‘Green’ across the entire DataFrame:

  first_set  second_set
0     Green      Yellow
1     Green      Yellow
2     Green      Yellow
3     Green       White
4     Green       White
5     Green       Green
6     Green       Green
7     Green       Green

How do you change a column value?

How do you change a value in a Python code?

How do I edit a column in a DataFrame in Python?

How do I change a DataFrame value in Python?

How do you replace a specific value in a DataFrame?

How do you change the values of a column in pandas based on condition?