Operators with Lists (and Tuples)

In this lesson we will apply a few of the operators we have learned to lists. The operations we will look at can also be applied to tuples.

Addition +, multiplication *, and equality == with lists

Let's consider two lists, x and y. If we apply the addition operator + to these lists, then we will get a new list that contains the elements of both lists combined. Multiplication with a list, same as a string, will repeat the list that number of times. Equality with a list will return True if all of the elements within the lists are the same, and False otherwise.

Using Numpy with lists

The above operations may have been surprising, after all, what if we want to perform element-wise arithmetic operations on the elements in a list? Using the basic arithmetic operators like + directly on lists results in concatenation rather than element-wise addition. To achieve element-wise operations, we can utilize a library called NumPy, which provides a wide array of functions for working with data structures such as lists.

NumPy is a library that provides many useful functions for working with lists and other data structures. Let's see how we can use NumPy to do element wise addition, subtraction, multiplication, and raise to the power of. We may access the NumPy library by importing it with the line import numpy as np. Note that we use something called an alias, np, to refer to the library. This is a common practice when importing libraries. Then we may access any functions within the library by prefacing it with a period.

  • addition: We can use the np.add function to add the elements of two lists together.
  • subtraction: To do subtraction the np.subtract function can be used to subtract the elements of the second list from the first list. In this example we pass in the single value 2, where NumPy treats this as a list of 2s.
  • multiply: Multiplication can be done with the np.multiply function.
  • power: And we can use the np.power function to raise the elements of the first list to the power of the second. Again, NumPy treats the single value 2 as a list of 2s.

Practice Question

Suppose lists year01_sales and year02_sales are lists containing the sales for each month of the year. Which of the following operations will calculate the average monthly sales?

score: 0%

Let's see how operators can be used with sets in the next lesson.