Indexing
Understand how DataFrame values can be accessed via indexing.
We'll cover the following...
Chapter Goals:
- Learn how to index a DataFrame to retrieve rows and columns
- Write code for indexing a DataFrame
A. Direct indexing
When indexing into a DataFrame, we can treat the DataFrame as a dictionary of Series objects, where each column represents a Series. Each column label then becomes a key, allowing us to directly retrieve columns using dictionary-like bracket notation.
The code below shows how to directly index into a DataFrame's columns.
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df = pd.DataFrame({'c1': [1, 2], 'c2': [3, 4],'c3': [5, 6]}, index=['r1', 'r2'])col1 = df['c1']# Newline for separating print statementsprint('{}\n'.format(col1))col1_df = df[['c1']]print('{}\n'.format(col1_df))col23 = df[['c2', 'c3']]print('{}\n'.format(col23))
Note that when we use a single column label inside the bracket (as was the case for col1
in the code example), the output is a Series representing the corresponding column. When we use a list of column labels (as was the ...