Book Image

Pandas 1.x Cookbook - Second Edition

By : Matt Harrison, Theodore Petrou
Book Image

Pandas 1.x Cookbook - Second Edition

By: Matt Harrison, Theodore Petrou

Overview of this book

The pandas library is massive, and it's common for frequent users to be unaware of many of its more impressive features. The official pandas documentation, while thorough, does not contain many useful examples of how to piece together multiple commands as one would do during an actual analysis. This book guides you, as if you were looking over the shoulder of an expert, through situations that you are highly likely to encounter. This new updated and revised edition provides you with unique, idiomatic, and fun recipes for both fundamental and advanced data manipulation tasks with pandas. Some recipes focus on achieving a deeper understanding of basic principles, or comparing and contrasting two similar operations. Other recipes will dive deep into a particular dataset, uncovering new and unexpected insights along the way. Many advanced recipes combine several different features across the pandas library to generate results.
Table of Contents (17 chapters)
15
Other Books You May Enjoy
16
Index

Reducing memory by changing data types

pandas has precise technical definitions for many data types. However, when you load data from type-less formats such as CSV, pandas has to infer the type.

This recipe changes the data type of one of the object columns from the college dataset to the special pandas categorical data type to drastically reduce its memory usage.

How to do it…

  1. After reading in our college dataset, we select a few columns of different data types that will clearly show how much memory may be saved:
    >>> college = pd.read_csv("data/college.csv")
    >>> different_cols = [
    ...     "RELAFFIL",
    ...     "SATMTMID",
    ...     "CURROPER",
    ...     "INSTNM",
    ...     "STABBR",
    ... ]
    >>> col2 = college.loc[:, different_cols]
    >>> col2.head()
       RELAFFIL  SATMTMID  ...       INSTNM STABBR
    0         0     420.0  ...  Alabama ...     AL
    1         0     565.0...