Filter (higher-order function)

Imagine you have a big basket full of fruits. Some of the fruits are apples, some are oranges, and some are bananas. You want to separate the apples from the other fruits and put them in a separate basket.

Now, think of the basket of fruits as a list of items in a computer program. The apples are what we call the "items" we want to extract from the list or, in computer terms, "filter" from the list.

To filter the list, we can use a "higher-order function." A higher-order function is like a special tool that helps us do something with a list. Just like how you use a spoon to eat soup.

So, the "filter" function helps us create a new list that only contains the items we want, in our case, only the apples. The filter higher-order function goes through each item in the list, one by one, and asks a question: "Is this item an apple?" If the answer is "yes," then it puts that item in a new basket or, in computer terms, a new list. If the answer is "no," then it moves on to the next item until it has gone through all the items in the original list.

By using the filter higher-order function, we can separate things in a list that we want from the things we don't want. It's like a magic wand that helps us clean up our lists and make them more organized. So that's why we call it a higher-order function - it helps us do something special with our lists.