Hey, what's going on everybody? So today I'm going to be explaining 2D lists. 2D meaning two-dimensional.
You do also have the capability of creating 2D tuples. I thought today we would use 2D lists just because they're pretty flexible. A two-dimensional list is just a list made up of lists.
It's really useful if you ever need a grid or matrix of data, kind of like an Excel spreadsheet. Let's create three lists. A list of fruit, vegetables, vegetables. and meat. I'm going to speed up this video, feel free to pause if you need to catch up.
Here I have three lists, a list of fruit, vegetables, and meat. Each of these lists is a one-dimensional list. To create a two-dimensional list, well, you would begin by creating a one-dimensional list.
Let's create a list of groceries. All I would need to do is add my individual lists as elements to the outer list, the 2D list. We have fruits, vegetables, and meats. Normally to print a list, or your other collections, you would print the name of the list.
In my list fruits I have apple, orange, banana, coconut. To access or change one of the elements, you would type the name of the list, then use the index operator. So fruits at index of 0 is a pineapple again. With a 2D list it's a little different.
If I were to print my 2D list of groceries, We would lay out the entire 2D list flat. We have individual lists, separated with a comma, all enclosed within a set of square brackets. Taking the elements found within our 2D list, I'm going to line these up kinda like this.
If It kind of represents a grid or matrix with rows and columns. Each individual list resembles a row. Each element resembles a column. If I were to print groceries at index 0, in place of returning one element found within one of the lists, that would return an entire row. So groceries at index 0...
is my fruits list. Groceries at index 1 is my vegetables list. Groceries at index 2 is my meats list. For one of the elements found within one of the rows, you would need two indices.
If I need the apple from the first row within my 2D list of groceries, that would be row zero, column zero. It's kind of like coordinates. Row zero, column zero, that would be my apple.
0, 1, which is an orange. 0, 2 is banana. 0, 3 is coconut.
For the next row, I would set the first index to be 1. Row 1, column 0, that would be celery. I'm going to speedrun this real quick just to show you all the different elements. 1, 1 is carrots. 1, 2 is potatoes.
If we try to access 1, 3... that index is out of range because we only have three elements within this row. So then the next row would have an index of two.
Column zero would be chicken. Two one is fish. Two two is turkey. 2, 3 is out of bounds. To access an element from a 2d list, you would need two indices in place of one, because using just one would return the entire row, like so.
Now when you declare a 2d list, you don't need to necessarily give each inner list a name. We could do something like this. I'm going to replace these names with the rows.
I'm just going to put these on a new line to make it more readable. There, that would work too. Just separate each inner list with a comma, then enclose everything with a set of square brackets. If you ever need to iterate over the elements of a 2D list, you can use nested loops.
If I were to use a single for loop, let's say for every, uh, maybe collection. For every collection in groceries, let's print what our collection is. Using a single for loop would iterate over the rows, but to also iterate over the elements found within each row We would use a nested loop for every food in our collection Let's print what our food is. Using nested loops we can iterate over all of the elements found within our 2d list, but I'm going to make this more organized like that grid structure we have. I'm going to replace the new line character at the end of a print statement with a space.
Then when we exit the nested loop I will print a new line by using just an empty print statement. There, that kind of resembles our grid structure. We have rows, and we have columns. With two-dimensional collections, you're not limited to just lists.
You could create a list of tuples, so the inner rows will be surrounded with a set of parentheses. You know, this is also valid too. Or you could make a 2D tuple.
It's a tuple that's made up of tuples. You could make a tuple made up of sets. Sets are enclosed with a set of curly braces.
Here we have a tuple made of sets. Use whatever is best for your own programs. Let's go over an exercise. Let's create a two-dimensional keypad that you would normally find on a phone. We have three data types.
A list, a set, and a list. set or a tuple. The elements in a set are unordered, so we can't use that. These numbers need to be in order.
If we have the option, a tuple is faster than a list. A tuple is ordered and unchangeable, so we should use it if we can. And that's perfectly fine. Let's create a 2D tuple this time.
I will name this 2D tuple numpad. We have an outer set of parentheses, then an inner set of parentheses for each row. We will have four rows.
The first row will be 1, 2, 3. The second row, I'm going to put this on a new line, 4, 5, 6. The next row will be 7, 8, 9. Then the last row will be an asterisk character, then 0. then the pound sign. So numpad in this case is a 2d tuple. Let's use a for loop to iterate over every row. This will be the outer loop. For every, maybe row, for every row in numpad, let's begin by printing our row.
So we're printing every row in our numpad, but I'd like to remove the parentheses. Let's create a nested loop for every... maybe num. For num in row. Print whatever that num is.
We have one long vertical line. Let's replace the newline character at the end of our print statement with a space. Then when we escape the nested loop, let's print a new line. And there is our telephone number pad.
You can see it's a grid made up of rows and columns. So yeah, that's a 2D list. Well, a 2D collection.
It's a collection that's made up of collections. Then with our numpad, we made a 2D tuple. If you ever need a grid or matrix of data, a 2D collection would work perfect. And there you have it, everybody. Those are 2D collections in Python.