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So this time around, I want to look at a couple of different data structures, half of what you'll



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be doing when you're writing programs is figuring out what kind of structure you want to store your



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data.



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And so far, we've seen some simple variables.



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And what I have here is just I've I've just taken everything out of the main function, deleted all



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the all of the other functions.



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And I just have one go file mango in package main with an empty main function.



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So what we've seen so far is just how to create variables so we can create a string variable like this



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via my string type string or we can create another variable var my input type it and we can store things



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in those by going my string is equal, too high and my input is equal to 11 and we have float's and



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other types as well.



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We also learned a shorthand for declaring a variable like my second string is equal to



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another string.



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And of course, the assignment variable has to have a colon before the equals sign, and then we can



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print those things out.



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Log, print line and just put all the variables in there, my string, my second string and my aunt.



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And that program will run just fine.



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So if I run that go, run, maned go, it'll just print those variables out as it does.



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So that's one way of storing data in simple variables.



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But sometimes you don't want to do that.



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Sometimes you want to have different data structures and we're going to look at to this time around.



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So let me delete all of this and show you how to create a map.



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First of all, what is a map?



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Well, let's make one.



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We'll call it my map.



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And I'll do the shorthand is equal to make a map, string, string.



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So I've created a map, but what is it?



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Well, the syntax for creating it is like this.



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You can if you want to go over my other map, map, string, string.



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But what you've done there is you've created a map that you can't actually do anything with.



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You don't create maps that way.



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There may be a certain really rarified set of circumstances where you'll find you find that an appropriate



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action.



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But I have yet to encounter it.



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So this is not how you declare a map.



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I'm going to get rid of that because that's not how you do it.



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You create a map this way using the shorthand syntax as the most common way of doing it.



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You use the make keyword and it's a built in function.



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You can read about it here just by rolling your mouse over it and reading that if you wish.



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But you actually create a map using this kind of of of syntax.



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So the first thing what you see in the square brackets here is actually the index that you use to look



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up the map.



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And what's following it is the value that is stored at that index.



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So I can do this now, my map dog and then my dog's name is equal to Sampson and then I can print that



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log dot print line, my map dog, which I better use the right case because in this case center and



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if I run this program, which I'll do right now, go run main go, it'll print out Sampson.



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What it's what I'm telling log print line to do is go to the map my map, find the key in that map called



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dog and print the value of it.



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I could even add something else to this.



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My map other dog is assigned the value of Cassi and if I duplicate this line and look up that key other



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dog, then it will print out first of all, Sampson, then Casy go run.



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Bingo, Sampson, Cassi.



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I can store as many things as I want in this map and I'm always going to store it using that key.



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So now what happens if I overwrite one of the keys?



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My map dog is equal to phyto.



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Well, what do you think's going to happen exactly?



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What's going to happen is exactly what you think is going to happen.



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It's going to replace the value of the key dog.



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It used to be Sampson.



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It'll put Fido there instead.



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So when I run this program now, go, run main go, it'll print Fido and Kassi.



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So that's what a basic string map is.



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But you can have other types of maps, so let's delete everything here.



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And instead of saying my map is a type of map, string, string, I can make it, my map is a type of



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map, string it and then I can put a couple of values in my map.



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First is going to equal to one and my map second is going to equal to two.



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And now if I put my log print line in here, logged print line my map first and then I print right after



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that, my map.



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Second, with a capital S. It'll print out one and then two, let's run it and make sure it does, I'll



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clear the screen.



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Go Roumain, go one, two.



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Exactly what you want.



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Now a map can store anything.



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So if, for example, I get rid of this and get rid of this and define my own type so I'll make a type



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type user is a struct.



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And inside of that, I have first name, which is a string and last name, which is a string, and then



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down here I made it make this a type of map, string, yuzu.



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I can do that.



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I create my own data type and I can store that in a string.



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So if I create a user, so I'll say me is assigned assigned type of user.



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And in that I put first name Trevor.



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Last name Sawalha.



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And then put a comma at the end, so it passes and then I say my map to me is equal to me and then log



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that print line.



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I can look up that value by saying my map.



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And the key, it is me dot first name.



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And if I run this go run mango, it should protect out Trevor, and it does so you can store whatever



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you want in a map, even types that you create yourself and maps are extremely useful because they're



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very, very fast.



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And one of the other nice things about maps is they're immutable.



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So in a lot of cases, when you're passing information around in a program, for example, you might



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create a structure or a variable or whatever it is.



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So let's just create a var my new car is of type.



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Oh, let's call it float 32 and my new Neuvirth



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is equal to eleven point one.



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No problem.



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I might want to pass that value, but I might want to pass a pointer to that value because I want to



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make sure when I pass that variable around to another function or another package that I'm actually



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passing a pointer to it.



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So when it's changed in the other package or changed in another function, I know it's going to affect



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the one that I created here.



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But you don't have to do that with maps because maps stay the same no matter where they go.



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You never have to bother pointing a passing a pointer to a map.



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You can just pass the map itself and that map will remain constant no matter where in the program it



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is accessed.



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That's extremely useful.



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Another point to know about maps is maps are programmatically built into the system, not sorted.



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So if you put things into a map in a certain order and then you try to access them later on, you cannot



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assume that they are going to be in the order.



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You originally added that you always must look up by key.



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That's a key thing to bear in mind.



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It used to be in the early days ago that people found a way that the hey, if I put things in a map,



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I can always get them out in the same order I put them in.



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And then the creators of Go said, no, we don't want you to do that.



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And in fact, we're going to sort them or we're going to randomize them on purpose.



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So you can't depend upon a map always being in the same order.



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So that's one thing to bear in mind about maps.



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OK, so maps are pretty straightforward and you always make it using this syntax make map.



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What do you want to look it up by?



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I usually use a string in most cases because it's easy to look up things by strings, but you can put



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an integer in there if you want to or whatever you want.



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Anything you can use as unique key for that map and then you can store whatever data type you want in



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there.



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If you don't know what data type you you're going to be storing in there, you can in fact, and this



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is not recommended, but you can put in type interface followed by an opening and closing curly brackets,



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and that will actually store anything you want.



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The problem is you have to cast it from what it is in the map back into what it needs to be in order



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to be useful for you.



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So this is really kind of a kludge, and I wouldn't do that.



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I would always use something else.



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So in here I had a string.



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I can put it back to a string and now or how to use or I guess and now everything works.



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All right.



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So that's maps.



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Let's get rid of this and let's talk about slices.



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Another thing you're going to run into quite regularly now from other programming languages.



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You're probably if you've worked in another programming language, you're probably familiar with the



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concept of an array and an array is is a data structure that can hold many elements just like a map,



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except that an array can be sorted but can go.



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We almost never use arrays.



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Instead we use slices.



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And here's how it works.



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So remember, we can we can create a variable that's a string by saying via my string of type string.



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And in that I can I can store one value so I can put my string is equal to fish and that's fine.



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No semicolon and then I can print that out log, print line my string so we know what that's going to



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do.



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We've done that many times already.



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But what happens if you want to store more than one string in a variable so you might have a selection



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of users, for example.



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So they might be just first names.



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So I want to have a variable that will store more than one string, which happens to be a first name



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in the same place.



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00:11:30,740 --> 00:11:36,890

Well, I can do that simply by putting these characters in front of the variable name.



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This is now a slice of strings, which means I can put more than one thing into it.



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Well, how do you add something to a slice that's not actually not that hard?



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I can simply say my string, which I'm going to rename to my slice, we'll call it my slice, rename



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it here equals append to put on the end of the slice.



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The slice I want to append to which is my slice.



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It's the only thing I have here and some value so.



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My name there and now what happens if I try to print that slice out?



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Let's run this program and find out.



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Go run Mango and it prints out.



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See how it put the braces, the square brackets around it, Trevor.



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Well, let's put another value in the string, John, and now run it again and I'll clear the screen



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so we can see it more easily.



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Now, it has two values, Trevor and John.



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I can put a third value in there, Mary and run it again.



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Go Roumain.



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Go Trevor.



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John and Mary.



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So now I have a data type called a slice, and this happens to be a slice of strings where I can put



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multiple values.



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Well, what if I change this from a slice of strings to a slice of it?



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Well, first of all, I only get three errors, but I can put two.



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One.



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And three and now if I run this, I should see two, one, three in exactly the order that I added them



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to one three.



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That was great.



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Can I do anything to a slice while we can find out really easily type of my slice followed by Duck and



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then we have append a time to sign cap copy for four.



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We have all kinds of things we can do to it.



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Pretty line.



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00:13:30,040 --> 00:13:31,370

What's this one sought.



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Let's try sorting it.



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Sort in my slice.



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Well, let's store that somewhere.



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Sorted is assigned sort since my slice.



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00:13:44,740 --> 00:13:45,910

No, that's not what it does.



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00:13:45,970 --> 00:13:46,740

Let's try it again.



190

00:13:47,140 --> 00:13:50,620

Let's just run it like this is it looks like it's actually going to sort the.



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It's in my slice.



192

00:13:53,020 --> 00:13:54,750

Let's run the program now.



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00:13:54,790 --> 00:13:58,090

Last time we got two, one, three, the order we put them in.



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00:13:58,120 --> 00:14:01,020

This time we get one, two, three.



195

00:14:01,030 --> 00:14:01,420

Look at that.



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I can sort a slice that works really well.



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So slices are extremely useful.



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And the great thing about them is you can declare it and then put as many values as you want in there.



199

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So that's an extremely helpful feature.



200

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Now, there are other ways of actually declaring slices, for example, I can use that shorthand, I



201

00:14:24,070 --> 00:14:33,310

can say, for example, numbers he's assigned and this time I'm going to go slice of it and then I will



202

00:14:33,310 --> 00:14:34,320

put some numbers in there.



203

00:14:34,330 --> 00:14:43,430

So one, two, three, four, five, six, seven, eight, nine, eight, eight, nine and 10.



204

00:14:44,080 --> 00:14:45,450

So now I have a slice.



205

00:14:45,460 --> 00:14:51,600

I've used the shorthand to actually declare a slice of INTs and then I pre populated it with ten values.



206

00:14:51,880 --> 00:15:01,690

So if I put that out, I can go log the print line numbers and reformat to make sure that my imports



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are right.



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They are.



209

00:15:02,590 --> 00:15:06,060

And that should print out the numbers from one to 10 with square brackets around it.



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And it does.



211

00:15:08,260 --> 00:15:12,790

What if I only want to say look at a range of that?



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Well, I can do that.



213

00:15:14,020 --> 00:15:15,490

Let's say I want to print the first three.



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I can say log print line and this time I want to go numbers, but only the first three and slices like



215

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arrays start counting at zero.



216

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So I can say from zero to two.



217

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And when I run the program this time I get just the first two numbers.



218

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I can go somewhere in the middle, I can go from six to eight or nine.



219

00:15:41,320 --> 00:15:42,070

I guess I typed nine.



220

00:15:42,080 --> 00:15:45,310

So we're going to go with nine, which should give me the last few bits.



221

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And it does seven, eight, nine.



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00:15:49,730 --> 00:15:55,280

All right, so that works reasonably well and slices will be extremely helpful for you.



223

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And just as you can have a map of different types, we can have a slice of different types.



224

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So if I delete everything and go, my child, do use the shorthand again, names is equal to a slice



225

00:16:07,070 --> 00:16:08,090

of string.



226

00:16:08,540 --> 00:16:16,950

And then in curly brackets, I put in some strings, one seven fish cap.



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Now I've created a slice of strings and I can actually print that out, a catalog print line and I'll



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print out names.



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And if I run this, I'll clear the screen.



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Run the program.



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Away we go.



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One seven fish cat so slices you'll be using them all the time will be using them regularly as we go



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through this course and we start, for example, pulling information out of the database.



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Sometimes when you access one thing from a database, you want one thing from a database, but very



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often you want to say go to the user's table and get me all of the users that have the status of inactive.



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And what we're going to give back is a slice of users in that case.



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But we got a little bit to cover before we can get that far along.



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But for right now, we have two new data types at our disposal, maps and slices.