Bags II

Last chapter teased the idea of naming the elements inside your bag. Like we give names to things in the real world. Or like putting a label / tag on it.

Most will read that sentence and immediately think: “that’s way more useful than giving them numbers!” But it’s actually a tie. Sometimes you want the elements numbered, sometimes you want them named.

Why?

• Naming things is extra work. If not needed, save yourself that work
• Numbers are easier to loop through (just use the iterator!)
• Numbers can be ordered/sorted.

For example, say your bag holds a list of people in your company, sorted by how long they’ve worked there. You want to get the person who has been at your company the longest. That’s the first one of the bag! If it’s numbered, the code is easy: peopleBag's 0. But if you used names … what’s the first one? Pieces of string don’t allow that sorting.

Nevertheless, there are situations where names are a godsend.

• They make your code more natural to read.
• When order doesn’t matter, it provides more information at no cost.

So how do we give names?

Give a name to an element with NAME means ELEM

In this shopping list, order is irrelevant. The price doesn’t change whether you added that T-shirt first or second. Instead, we’re just interested in what is inside. And its properties: in this case, the price of each element.

With a setup like this, code becomes easy to read.

Looping through bags II

Because bags and loops go hand in hand, most languages have easier ways to loop through all of the bag.

Now that you know about named bags, you’ll see there are two ways to loop through one.

• You can loop through its names (or indices, or labels)
• You can loop through its values (or elements, or items)

Whichever you want depends on the use case. But I can’t count how many times code failed spectacularly (for me or new coders) because they picked the wrong thing over which to iterate.

To get a bag’s labels, use BAGNAME's labels

To get a bag’s items, use BAGNAME's items

Bag

 => 

Bag

But let’s think about this. We just received another list of values. Because, well, the bag has multiple items/labels! So we just received another bag.

What’s the difference? This bag is always numbered. It’s a “simpler bag” if you will. One that’s 100% ready to be used in a loop!

You can do this the usual way.

However, as you know by now, most languages provide quicker ways. A fancier syntax for this very common use case.

To loop through a numbered bag, use search BAGNAME

The value is available as bamboo value.

Remember that we’re now going over a numbered bag. We’ve prepared it for our loop! So the index (or the “label”) is just your same old bamboo iterator.

About notation

Hopefully, you see my reasoning for picking my syntax.

I call these things bags, because they are a container that can hold anything. Any number of elements, any size, any shape.

I use the possessive syntax ('s) because it leads to a readable, English sentence.

In other languages, these examples would be littered with symbols and syntax. This isn’t bad. Once you do more programming, you will understand why this is the case. (They make coding faster, more precise and less verbose.)

But it is bad for someone new to programming. This course aims to explain the underlying intuition for programming, without overwhelming you.

If you really want to know, here’s how you’d write the above in JavaScript. (A language that, all things considered, is also relatively accessible and readable.)

1const backpack = {
2  "jacket": "Optional",
3  "sleeping bag": "Necessary",
4  "toothbrush": "Necessary",
5  "teddy bear": "Nope"
6}
7
8console.log("My jacket is ... " + backpack["jacket"]);
9// or: console.log("My jacket is ... " + backpack.jacket);

Turtles all the way down

Now remember that a bag just holds other values. These can be anything. They can be a complex calculation, another variable—another bag.

Slowly, as you learn these advanced parts of coding, you’ll see the framework upon which complex programs are built. In a real web shop, a shopping list isn’t just item names + their price. Of course not—there’s way more going on!

Yes, the names are still the items. (Why change that? It leads to human readable code.)

But the values are other bags holding all sorts of information. The price of the item, but also how many are in stock, features, reviews, special discounts, statistics (like how many have been bought the past month), etcetera.

All code is built from tiny elements. Tiny pieces of data. But these elements are collected inside bags, inside bigger bags, inside even bigger bags, until you have a complex program doing a lot.

Exercises

As you do these exercises, always go one step further. After writing your code (that works for this specific list), change the list. Add entries, remove entries, change names. Your code should still work. Otherwise, it’s not general/logical enough.

Exercise 1

Create a bag that holds all 5 users of your app. Now loop through them and print their names.

Bag

 => 

Output

Exercise 2

Create that same bag of users, but now attach some info to each user: how many hours a week they use your app. Loop through it and only print those that spend at least 5 hours a week on your app.

Bag

 => 

Bool & Output