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IPython Interactive Computing and Visualization Cookbook

IPython Interactive Computing and Visualization Cookbook

By : Cyrille Rossant
4.5 (13)
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IPython Interactive Computing and Visualization Cookbook

IPython Interactive Computing and Visualization Cookbook

4.5 (13)
By: Cyrille Rossant

Overview of this book

Intended to anyone interested in numerical computing and data science: students, researchers, teachers, engineers, analysts, hobbyists... Basic knowledge of Python/NumPy is recommended. Some skills in mathematics will help you understand the theory behind the computational methods.
Table of Contents (22 chapters)
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IPython Interactive Computing and Visualization Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Making efficient array selections in NumPy


NumPy offers several ways of selecting slices of arrays. Array views refer to the original data buffer of an array, but with different offsets, shapes, and strides. They only permit strided selections (that is, with linearly spaced indices). NumPy also offers specific functions to make arbitrary selections along one axis. Finally, fancy indexing is the most general selection method, but it is also the slowest as we will see in this recipe. Faster alternatives should be chosen when possible.

Getting ready

We suppose that NumPy has been imported and that the id function has been defined (see the Understanding the internals of NumPy to avoid unnecessary array copying recipe).

How to do it...

  1. Let's create an array with a large number of rows. We will select slices of this array along the first dimension:

    In [3]: n, d = 100000, 100
    In [4]: a = np.random.random_sample((n, d)); aid = id(a)
  2. Let's select one row from every 10 rows, using two different methods...

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