What is the method for altering a pandas dataframe one slice at a time?

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The method for altering a pandas dataframe one slice at a time is to use the loc method. The loc method allows you to access a subset of the dataframe by specifying the row and column labels. You can then modify the values in the subset using standard assignment statements.

For example, let's say you have a dataframe called df and you want to change the value of a specific cell in the dataframe. You can do it as follows:

# create a dummy dataframe import pandas as pd df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6], 'c': [7, 8, 9]}) # change the value at position (1, 'b') to 10 df.loc[1, 'b'] = 10 

This will change the value at position (1, 'b') in the dataframe to 10. You can use similar syntax to modify a range of rows or columns. For example:

# change the values in column 'c' for rows 0 and 1 df.loc[0:1, 'c'] = [10, 20] 

This will change the values in column 'c' for rows 0 and 1 to 10 and 20, respectively.