We can easily add new columns to an existing DataFrame using the indexing syntax:

dataframe[column_name] = values

It is important that if values is a list, it needs to have the same number of elements as there are rows in the DataFrame, otherwise you'll get an error. Alternatively, we can assign a single value to the entire new column as well.

Example 1: New Column from a Single Value


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import pandas as pd

df = pd.DataFrame({
    'Product': ['Laptop', 'Tablet', 'Phone'],
    'Old Price': [1000, 600, 400]
})

# Add a new column with a fixed price for all rows
df['New Price'] = 700

print(df)

Example 2: New Column using a List of Values


              1234567891011
            
import pandas as pd

df = pd.DataFrame({
    'Member': ['Sophie', 'Liam', 'Emma'],
    'Role': ['Designer', 'Developer', 'Tester']
})

# Add a new column for Project Name
df['Project'] = ['Marketing Website Redesign', 'Client Portal Backend Development', 'Payment Flow QA Testing']

print(df)

Example 3: New Column derived from Another Column


              1234567891011
            
import pandas as pd

df = pd.DataFrame({
    'Product': ['Laptop', 'Tablet', 'Phone'],
    'Price': [1000, 600, 400]
})

# Derive a new column 'Discounted Price' (10% off)
df['Discounted Price'] = df['Price'] * 0.9

print(df)

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?

3. What would be the output of the following code?

Which of the following lines correctly adds a column Discount which is 20% of the Price?

Select the correct answer

df['Discount'] = df['Price'] - 0.2

df['Discount'] = df['Price'] * 20

df['Discount'] = df{Price} * 0.2

df['Discount'] = df['Price'] * 0.2

What would be the output of the following code?

Select the correct answer

       Item  Price  Final Price
0   Monitor    200        210.0
1  Keyboard     50         55.0
2     Mouse     25         27.5

       Item  Price  Final Price
0   Monitor    200       220.0
1  Keyboard     50        60.0
2     Mouse     25        30.0

       Item  Price  Final Price
0   Monitor    200       200.0
1  Keyboard     50        50.0
2     Mouse     25        25.0

       Item  Price  Final Price
0   Monitor    200        20.0
1  Keyboard     50         5.0
2     Mouse     25         2.5

¿Todo estuvo claro?

¡Gracias por tus comentarios!

Sección 2. Capítulo 5

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We can easily add new columns to an existing DataFrame using the indexing syntax:

dataframe[column_name] = values

Example 1: New Column from a Single Value


              1234567891011
            
import pandas as pd

df = pd.DataFrame({
    'Product': ['Laptop', 'Tablet', 'Phone'],
    'Old Price': [1000, 600, 400]
})

# Add a new column with a fixed price for all rows
df['New Price'] = 700

print(df)

Example 2: New Column using a List of Values


              1234567891011
            
import pandas as pd

df = pd.DataFrame({
    'Member': ['Sophie', 'Liam', 'Emma'],
    'Role': ['Designer', 'Developer', 'Tester']
})

# Add a new column for Project Name
df['Project'] = ['Marketing Website Redesign', 'Client Portal Backend Development', 'Payment Flow QA Testing']

print(df)

Example 3: New Column derived from Another Column


              1234567891011
            
import pandas as pd

df = pd.DataFrame({
    'Product': ['Laptop', 'Tablet', 'Phone'],
    'Price': [1000, 600, 400]
})

# Derive a new column 'Discounted Price' (10% off)
df['Discounted Price'] = df['Price'] * 0.9

print(df)

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?

3. What would be the output of the following code?

Which of the following lines correctly adds a column Discount which is 20% of the Price?

Select the correct answer

df['Discount'] = df['Price'] - 0.2

df['Discount'] = df['Price'] * 20

df['Discount'] = df{Price} * 0.2

df['Discount'] = df['Price'] * 0.2

What would be the output of the following code?

Select the correct answer

       Item  Price  Final Price
0   Monitor    200        210.0
1  Keyboard     50         55.0
2     Mouse     25         27.5

       Item  Price  Final Price
0   Monitor    200       220.0
1  Keyboard     50        60.0
2     Mouse     25        30.0

       Item  Price  Final Price
0   Monitor    200       200.0
1  Keyboard     50        50.0
2     Mouse     25        25.0

       Item  Price  Final Price
0   Monitor    200        20.0
1  Keyboard     50         5.0
2     Mouse     25         2.5

¿Todo estuvo claro?

¡Gracias por tus comentarios!

Sección 2. Capítulo 5

Adding new Columns

Example 1: New Column from a Single Value

Example 2: New Column using a List of Values

Example 3: New Column derived from Another Column

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?

3. What would be the output of the following code?

Awesome!

Adding new Columns

Example 1: New Column from a Single Value

Example 2: New Column using a List of Values

Example 3: New Column derived from Another Column

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?

3. What would be the output of the following code?

Adding new Columns

Example 1: New Column from a Single Value

Example 2: New Column using a List of Values

Example 3: New Column derived from Another Column

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column Discount which is 20% of the Price?

3. What would be the output of the following code?

Awesome!

Adding new Columns

Example 1: New Column from a Single Value

Example 2: New Column using a List of Values

Example 3: New Column derived from Another Column

1. What happens if you try to add a new column to a DataFrame with a list that has fewer elements than the number of rows?

2. Which of the following lines correctly adds a column Discount which is 20% of the Price?

3. What would be the output of the following code?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?

2. Which of the following lines correctly adds a column `Discount` which is 20% of the `Price`?