Python count elements in list with condition

How do I count items in a list based on a condition in Python.

There are many ways to count the occurrences of items in a list based on a condition. Here you will see two of them: one example with map and one example by using list comprehension.

Start by creating a list of names. Note that chuck appears twice in the list.

Count occurrences by using Map

By using map you can provide a lambda with the condition like this:

This results in a map object that we can inspect by converting it to a list:

You see that the map has converted the values in the list names to boolean values. If you replace list with sum, Python will calculate the total of True values:

Count occurrences by using List comprehension

List comprehension is another way to map lists to create new lists. You can start by using a list comprehension that does not filter the list at all and thus returns a copy of the original list:

To filter that list, you can use if:

Now use the len function to count the occurrences: