Python Indicator Function – Apply Indicator Function to List of Numbers

In Python, we can define and apply indicator functions easily. To apply an indicator function to a list of numbers using Python, the easier way is with list comprehension.

list_of_nums = [10,-4,2,0,-8]

indicator = [1 if x > 0 else 0 for x in list_of_nums]

print(indicator)

#Output:
[1, 0, 1, 0, 0]

An indicator function maps a set of numbers to the values 0 and 1.

In Python, we can define our own indicator functions and apply them to lists of numbers.

One such indicator function is the function that if a number is positive, we should return 1, and if the number is not positive, then we return 0.

To apply this indicator function to a list of numbers, we can use list comprehension as shown in the following Python code.

list_of_nums = [10,-4,2,0,-8]

indicator = [1 if x > 0 else 0 for x in list_of_nums]

print(indicator)

#Output:
[1, 0, 1, 0, 0]

We can get the same result if we use a for loop, but list comprehension is easier to read and is less code.

list_of_nums = [10,-4,2,0,-8]

indicator = []

for x in list_of_nums: 
    if x > 0:
        indicator.append[1]
    else:
        indicator.append[0]

print(indicator)

#Output:
[1, 0, 1, 0, 0]

Applying a Complicated Indicator Function to a List in Python

If we have a more complicated indicator function, most of the time, it will be easier to code up the function and then use list comprehension.

For example, let’s say we have an indicator function which should be 0 if the number is less than -10, 1 if the number is between -10 and 10, and is 0 if the number is greater than 10.

While it’s possible to do this in one line, it’s easier to follow if we define a function which defines the indicator function, and then we can apply it to each element of a list.

Below is the indicator function in Python for our example.

def indicator_function(num):
    if num < -10 or num > 10: 
        return 0
    else:
        return 1

We can apply this function now on a list of numbers.

list_of_nums = [15,-4,12,0,-8]

indicator = [indicator_function(x) for x in  list_of_nums]

print(indicator)

#Output:
[0, 1, 0, 1, 1]

Hopefully this article has been useful for you to understand how to use list comprehension to apply an indicator function in Python.