Data Manipulation II

In the Strings chapter, I promised some more “bag-like” operations to do on strings. They can be extremely important or not important at all, depending on your project. Still, all languages support them, and I wanted to end the course with these.

I’ve explained how strings are sort-of “bags of characters”. The string panda is also p, a, n, d, a.

But it goes even further than that! Because what’s stopping us from grouping the characters in a different way? Why not pan and da?

These are called substrings. Even short strings—like panda—have many different ways to select characters.

Finding substrings

Let’s think back to our example from the original strings chapter. You’re running a website with a comments section.

But now you receive hundreds of spam comments every day! How to detect them?

You would have to

• Determine what words you consider “spam”
• Search the comment for those words as a substring

Sometimes, you just want to know if a substring exists. If a smaller word is inside another word. But more often than not, you’re more interested in where it is.

You want to receive the index where that substring starts. Just like the index for bags. The first character has index 0, the second index 1, and so forth.

To get the index of a substring in a string, use STRING's SUBSTR

String

 => 

Number

Remember that a substring can be one character or several characters—any string no larger than the original string.

What if the string isn’t there? The convention is to return the number -1. Other languages might return a “nothing” value.

So let’s see what we can do about those spam comments.

Selecting substrings (one char)

Let’s start with the simplest version. Most languages have a special syntax for this, as it’s so common. You just want to know what symbol is at a given index inside a string.

To get the symbol at an index ( = number), use STRING's IDX

String

 => 

String

For example, take that famous guessing game children play. You say a word. The next player must say a word that starts wit the final letter of your word. (I actually implemented something like this in a word guessing game once. This has a real use case in coding!)

How might you check if a word is valid?

Try it. Try changing the words. Maybe change the rules of the game: the second letter has to match the second to last of the previous word. Or the new word has to be the same _size as the previous one.

You cannot set ( = change) the character this way. I didn’t allow this, because no language allows this. It’s a tough thing to implement and it has many nasty side effects. Instead, strings are immutable by default: you can’t change them. Instead, if you want a changed version, you always create a new string the way you like.

Selecting substrings (substring)

This is perhaps the most complex string transformation. To select exactly the substring you want from a bigger string. If you have to do this a lot, you’re most likely coding something the wrong way. But sometimes, once in a while, this is crucial to solving a problem.

To get only part of a bigger string, use select IDX1 to IDX2 from STRING

String

 => 

String

For example, I’ve used functions like these a lot while building my Bamboo language. (The one used in these examples.) Because what is a programming language? It’s just something that accepts one big string ( = your code) and chops it into pieces that it understands. All my system does is break your code into smaller and smaller strings, until I can select the parts I need to execute.

But let’s use a … smaller and simpler example than that.

Example: dense data

In online multiplayer games, you send information to a server (over the internet) and receive it while playing. This means there’s a time delay between doing something and your action reaching the server. This is called “latency”.

You obviously want this to be as low as possible. To achieve this, games don’t send everything over the internet. They don’t even send raw data.

Instead, they package the information into one tight string and send that. For example, user123/58/4,2,3

What does this mean?

• The player user123
• With health 58
• Is at coordinates X = 4, Y = 2 and Z = 3

All that information densely packed into a small string.

This is also used in many other applications where speed or latency are important.

The exercise here will not be surprising. Write a piece of code …

• To accept the string user123/58
• And break it into its pieces: username and health.

String

 => 

Two Values

Notice how we select the health starting from slashIndex + 1. Otherwise, we’d also select the actual slash (/) symbol.