pandas DataFrames

A pandas DataFrame is a data structure, which is a labeled two-dimensional object and is similar in spirit to an Excel worksheet or a relational database table. A similar concept, by the way, was invented originally in the R programming language. (For more information, refer to http://www.r-tutor.com/r-introduction/data-frame.) A DataFrame can be created in the following ways:

• From another DataFrame.
• From a NumPy array or a composite of arrays that has a two-dimensional shape.
• Likewise, we can create a DataFrame out of another pandas data structure called Series. We will learn about Series in the following section.
• A DataFrame can also be produced from a file, such as a CSV file.

As an example, we will use data that can be retrieved from http://www.exploredata.net/Downloads/WHO-Data-Set. The original datafile is quite big and has many columns, so we will use an edited file instead, which only contains the first nine columns and is called WHO_first9cols.csv; the file is in the...