What is idxmax() in Pandas?

What is idxmax() in Pandas?

In Pandas, the idxmax method is used to return the index of the row with the maximum value in a specified column.

For example, consider the following DataFrame:

import pandas as pd

df = pd.DataFrame({
    'A': [1, 2, 3, 4, 5],
    'B': [10, 20, 30, 40, 50],
    'C': [100, 200, 300, 400, 500]
})

This DataFrame has three columns A, B, and C, with five rows of data.

To find the index of the row with the maximum value in column B, you could use the following code:

import pandas as pd

df = pd.DataFrame({
    'A': [1, 2, 3, 4, 5],
    'B': [10, 20, 30, 40, 50],
    'C': [100, 200, 300, 400, 500]
})

# Find the index of the row with the maximum value in column B
max_index = df['B'].idxmax()

# Print the maximum value and its index
print(f'The maximum value in column B is {df["B"].max()} at index {max_index}.')

The maximum value in column B is 50 at index 4.

In the code above, the idxmax method is applied to the B column of the DataFrame. This returns the index of the row with the maximum value in that column. In this case, the maximum value is 50, and it is located at index 4.

The idxmax method can also be used with multiple columns.

For example, if you wanted to find the index of the row with the maximum value in either column B or column C, you could do the following:

import pandas as pd

df = pd.DataFrame({
    'A': [1, 2, 3, 4, 5],
    'B': [10, 20, 30, 40, 50],
    'C': [100, 200, 300, 400, 500]
})

# Find the index of the row with the maximum value in columns B and C
max_index = df[['B', 'C']].idxmax()

# Print the maximum value and its index
print(f'The maximum value in columns B and C is {df[["B", "C"]].max().max()} at index {max_index}.')

The maximum value in columns B and C is 500 at index
B    4
C    4
dtype: int64.

In the code above, the idxmax method is applied to the B and C columns of the DataFrame. This returns the index of the row with the maximum value in either of these two columns. In this case, the maximum value is 500, and it is located at index 4.

The idxmax method will return the index of the first row with the maximum value, in the case where there are multiple rows with the same maximum value.