Problem: How to create a sequence of evenly-spaced values
- Using pure, vanilla Python, and
- Using NumPy’s
linspace()method.
Example: Given three arguments: start=10, stop=20, number_of_values=11. How do you create a sequence of 11 values x0, x1, …, x10 where two subsequent values xi and x(i-1) have the same distance for all i in {0, …, 10}.
# Givenstart = 10 stop = 20 num_vals = 11# Desired magic_method(start, stop, num_vals) # Returns [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
Next, you’ll learn two methods that accomplish this goal!
Method 1: Vanilla Python
You can create a sequence of a certain number of evenly spaced floats in two steps:
- Calculate the difference between two subsequent numbers as
(stop-start)/(num_vals-1)assuming you want to include endpoints. - Create a list of evenly spaced numbers using list comprehension:
[start + i * delta for i in range(num_vals)]
# Problem Formulation start = 10 stop = 20 num_vals = 11 # Method 1: Vanilla Python delta = (stop-start)/(num_vals-1) evenly_spaced = [start + i * delta for i in range(num_vals)] print(evenly_spaced)
Method 2: NumPy linspace()
How does it work? Have a look at this graphic that explains NumPy’s linspace function visually:
It takes only three arguments in most cases: start, stop, and num. To accomplish the goal, you’d use the following code:
# Problem Formulation start = 10 stop = 20 num_vals = 11 # Method 2: NumPy Linspace import numpy as np print(np.linspace(start, stop, num_vals)) # [10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.]
Note that the result is a list of floats. To convert them to an int, you can use the following one-liner instead:
print([int(x) for x in np.linspace(start, stop, num_vals)]) # [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
NumPy linspace() Puzzle
Can you solve this Python puzzle?
[python]
import numpy as np
year = np.linspace(0, 365, 366)
print(int(year[-1] – year[-2]))
[/python]
Exercise: What is the output of this puzzle?
You can also solve it on our interactive Python puzzle app and track your Python skills here:
Numpy is a popular Python library for data science focusing on linear algebra.
This puzzle is about the useful function linspace. In particular, linspace(start, stop, num) returns evenly spaced numbers over a given interval [start, stop], with stop included.
For example, linspace(0,3,4) returns the numpy array sequence 0,1,2,3 (i.e., 4 evenly spaced numbers).
This function is particularly useful when plotting (or evaluating) a function. The result of the function applied to evenly spaced numbers reveals how it progresses for growing parameter values.