Key Concepts

Review core concepts you need to learn to master this subject

Indexing NumPy elements using conditionals

NumPy element-wise logical operations

Creating NumPy Arrays from files

NumPy Arrays

Accessing NumPy Array elements by index

NumPy element-wise arithmetic operations

Indexing NumPy elements using conditionals

numbers = np.array([-5, 4, 0, 2, 3])
positives = numbers[numbers > 0]
print(positives)
# array([4, 2, 3])

NumPy elements can be indexed using conditionals. The syntax to filter an array using a conditional is array_name[conditional].

The returned array will contain only the elements for which the conditional evaluates to True.

Introduction to NumPy
Lesson 1 of 1
  1. 1
    Introduction to NumPy: Numerical Python
    Sarah records her second-grade class’s grades in an online spreadsheet. Her web browser records that she visited that spreadsheet, in addition to every other site she’s visited. Those sites record…
    Start
  2. 2
    Importing NumPy
    To use NumPy with Python, import it at the top of your file using the following line: import numpy as np Writing as np allows us to use np as a shorthand for NumPy, which saves us time when cal…
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  3. 3
    NumPy Arrays
    NumPy includes a powerful data structure known as an array. A NumPy array is a special type of list. It’s a data structure that organizes multiple items. Each item can be of any type (strings, …
    Start
  4. 4
    Creating an Array from a CSV
    Typically, you won’t be entering data directly into an array. Instead, you’ll be importing the data from somewhere else. We’re able to transform CSV (comma-separated values) files into arrays usin…
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  5. 5
    Operations with NumPy Arrays
    Generally, NumPy arrays are more efficient than lists. One reason is that they allow you to do element-wise operations. An element-wise operation allows you to quickly perform an operation, such …
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  6. 6
    Operations with NumPy Arrays II
    Arrays can also be added to or subtracted from each other in NumPy, assuming the arrays have the same number of elements. When adding or subtracting arrays in NumPy, each element will be added/sub…
    Start
  7. 7
    Two-Dimensional Arrays
    In Python, we can create lists that are made up of other lists. Similarly, in NumPy we can create an array of arrays. If the arrays that make up our bigger array are all the same size, then it has …
    Start
  8. 8
    Selecting Elements from a 1-D Array
    NumPy allows us to select elements from an array using their indices. Consider the one-dimensional array a = np.array([5, 2, 7, 0, 11]) If we wanted to select the first element in this array, we…
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  9. 9
    Selecting Elements from a 2-D Array
    Selecting elements from a 2-d array is very similar to selecting them from a 1-d array, we just have two indices to select from. The syntax for selecting from a 2-d array is a[row,column] where a i…
    Start
  10. 10
    Logical Operations with Arrays
    Another useful thing that arrays can do is perform element-wise logical operations. For instance, suppose we want to know how many elements in an array are greater than 5. We can easily write som…
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  11. 11
    Review
    Let’s take a second and review. In this lesson, you learned the basics of the NumPy package. Here are some key points: - Arrays are a special type of list that allows us to store values in an orga…
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