To calculate the sum of values in a dataframe column in Python, simply use the sum() function on the column. In the example given, the sum of values in column 'C' would be 24.

This question is about how to round the values in a dataframe column to the nearest integer. The output should show the rounded values in the column.

Given a dataframe, find the row with the maximum value in column 'C' and return the values in columns 'A' and 'B' for that row.

To calculate the percent change in stock prices, we can simply subtract the stock price on the previous day from the stock price on the current day, and divide by the previous day's stock price .

This technical problem deals with how to keep only certain columns in a dataframe using Python. A function is provided that takes in a dataframe and a list of column names, and returns a new dataframe with only the columns in the list. An example is given of input and output.