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Start communicating ideas and diagramming data in a more interactive way. In this course, author Barton Poulson shows how to read, map, and illustrate data with Processing, an open-source drawing and development environment. On top of a solid introduction to Processing itself, this course investigates methods for obtaining and preparing data, designing for data visualization, and building an interactive experience out of a design. When your visualization is complete, explore the options for sharing your work, whether uploading it to specialized websites, embedding the visualizations in your own web pages, or even creating a desktop or Android app for your work.
In this movie, I want to talk about how you can work with variables specifically, modify their values over time, which of course is the flexibility that variables give you. What I want to demonstrate is how you can assign values several times to the same variable where the latest one trumps the previous one. And also, how you can change a variable from one type to another, and you can also create code to systematically change variables, as well as constrain some of their flexibility to keep them within a particular range.
So what I'm going to do is I'm going to start by titling this sketch and then, I'm going to declare a few variables that we saw in the last video. So I have an integer variable called x, I'm giving it an initial value of 10. We have a floating-point variable, a float variable called y, I'm giving it an initial value of 50 and then, we also have a float variable z.
I'm simply declaring it without initializing it. Next I'm going to create a drawing with two blocks of code. Now, we're going to talk more about the dynamic drawings in a later movie, but for right now, you need to know that I'm going to have one block that's called setup. By the way, the reason this says void at the beginning is because every function, and setup is a function, needs to have a return value type. If it doesn't return a variable, and this one doesn't, then you put void to indicate that there's nothing that comes back.
Also, it has empty parentheses because the function is supposed to have arguments and this indicates that there is a space there, but it doesn't have any. Instead, we're going to put everything about this function within these curly brackets. The first thing, I'm going to do is declare the size of the window. So I'm going to do size 600x200. I'm going to turn on anti-aliasing again to smoothen things out. I'm also going to turn off stroke, so there's no border outline around shapes. Now what I'm going to do is I'm going to assign a value to a variable.
Watch how we do this. Assign a new value to an existing variable. What I'm going to do is I'm going to take y, which previously I've initialized at 50, and I'm going to redefine it to be height. Height is a built-in variable and Processing knows that height is the height of the window, in this case, it's 200 pixels and width is how wide the window is, it would be 600.
So right now, I'm just setting y, changing it from the initial 50 here to be the height of the window. Next, I want to show you something about what's called casting a variable and that is sometimes a variable comes in one particular type and you want to change it to a different type. The most common is taking float variables which are decimal points and converting them to integer variables or int which don't.And so, the way I'm going to do is I'm first going to create a float variable. So it says randomFloat and I'll give it a random number from 0 to 10.
Now, the way the random function works here is it will take any number in-between there, and it uses decimal, so it's a floating point thing. 0, the lower end is inclusive, the upper end 10, is exclusive. So you can get a zero, you can't get a 10. You can get anything in-between. If I want to specify the lower value, if I want it to be like 5, I can simply type it in, 5 to 10 and I'll show you that in a later movie. What I'm going to do right now though is I'm going to do this little print line. Now, if I hit Run, you see in the Console that I have my randomFloat variable, that's good.
So that's down there. Now, let's say that I want to get a random integer from this that I want an actual number from 0 to 10. The way that I would do that is closely related. In fact, I'm just going to copy this text, paste it right here and then, this time I'm going to create, instead of randomFloat, I want a randomInteger variable. Now if I want to have 10 be a choice, the way Processing works, I actually need to go up to 11, because it doesn't include the 11, it goes up to 10.9999 and what the casting is going to do is it's going to chop off the decimal places and leave me with the part in front of that.
So all I need is this. And then what I'm going to do is I'm going to come over here, and tell it's an integer variable. I'm going to get an error message if I run this, see what happens. Because this is a float variable, random has decimal places, but I've declared an int over here, so that's just not going to work. So instead, what I do is I need to cast it into a different type. That's pretty easy. All you need to do in Processing is I put int and put the rest of this in parentheses, and it says take whatever is in there and turn it into an integer variable and it does this by simply chopping off the decimal places.
And so now, when I run this code, you see I now have a random number and it's just a 2. If you want to do something like roll dice, one option is to do it this way. I simply take this down here and I'll say I'm going to get a random die. Now, the difference here is that the dies only go from 1 to 6, whereas the numbers I've been using so far go from 0 to 10.
So I want a different range. What I'm going to do is because I don't want zeros, I want one ones, but I want to have 6 be an option, is if I put the limit at 6, it'll go from 0 to 5.99, it'll chop off the decimal places which may means it goes from 0 to 5. All I have to do then is add 1 at the end of it. And then if I take that and run it like this, you can see now that I have a number from 1 to 6, I can run this a few extra times and you'll see that I'll get different values, there is a 2 for the die, and there is 4.
It will stay within that range. Now I'm going to show you, you can actually get much more fancy in how you deal with your variables here. If we go to the top of the sketch, you will see I declared a variable z, but I didn't initialize it. Right down here, I'm going to get z and I'm just going to show you that things can get rather fancy. So I might say that z = 3*x, I have a value for x earlier, then I'm going to also add the arc tangent of the square root of y, it could come up you don't know and then, I run that variable, run the whole thing and there I have the arc tangent of the square root of y plus three times x, there maybe a situation which you need that, I don't know what it is right now.
The next thing is to show how to increment a variable overtime. What I want to show is in a separate block of code called draw. So I'm going to draw an ellipse and actually, if I want the ellipse to show, I need to refresh the background every time we go through, and then I show the ellipse, and then I'm going to give it these variable values of x, y and then make the ellipse 40 pixels tall and when I do this, it will draw a circle, you see my circle there in the bottom-left, but what I want to do is I want to make it that the circle can move and one way to do that is through incrementing it.
An increment takes a variable and adds a value to it every time it runs through a cycle. Here the ++ simply means add 1 to it. Also, you can do other kinds of increments. So for instance on this one, I'm going to take the value for y, the height, and I'm going to multiply it times a particular time, every time we go through it this one. I'm actually going to do a 0.99 and what this means is that the height is going to actually decrease. It's going to be 99% of its initial value every time. And when I draw that, you see that this now moves.
Now it's going to keep moving until it disappears. If I want to try to keep it in place, all I need to do then is what's called the constrain and I can go x = constrain(x -- so x is referring back to itself. I'm going to constrain x, the lowest value it can have is 0 and the highest it can have is the width of the window divided by 2.
So it'll stop when it gets halfway. I save this and run it, and you see it goes up until it gets halfway and it's just going bonk into it and stop. Anyhow, these are a few different ways of working with variables and modifying them to make it, so they can take on new values and give some flexibility to how you work with your information in your sketch.
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