WEBVTT 00:00.360 --> 00:01.350 Welcome back. 00:01.530 --> 00:05.010 I want to talk to you quickly about something called Matrix. 00:05.750 --> 00:15.380 And a matrix is a way to describe 2D lists or multi dimensional lists. 00:15.410 --> 00:16.310 What do I mean? 00:16.490 --> 00:24.620 Well, I can create a matrix, and this is a name that I just made, so I can call it whatever I want. 00:24.650 --> 00:27.350 But usually these are called matrix and programming. 00:28.050 --> 00:29.660 And it looks something like this. 00:29.670 --> 00:30.870 It's an array. 00:31.560 --> 00:33.480 With another array inside of it. 00:34.530 --> 00:36.420 So let's say, for example. 00:39.400 --> 00:41.320 I have one, two, three here. 00:42.310 --> 00:47.410 And then another array one or let's do two for. 00:48.470 --> 00:49.220 Six. 00:50.110 --> 00:52.020 And then another array. 00:52.030 --> 00:54.280 Seven, eight, nine. 00:55.190 --> 00:56.510 What's happening here? 00:56.870 --> 00:59.360 Well, it's a two dimensional array. 00:59.540 --> 01:02.300 We have the main array. 01:03.240 --> 01:07.590 And then we have sub arrays, three arrays to be exact. 01:07.830 --> 01:10.230 Now, why is this useful? 01:10.350 --> 01:15.240 And by the way, this is two dimensional, but we can have multiple ones. 01:15.240 --> 01:19.350 For example, you can have another array inside of this array. 01:21.560 --> 01:23.360 But why is this important? 01:24.500 --> 01:31.280 These type of matrices come up a lot in topics like machine learning or image processing. 01:31.760 --> 01:36.320 For example, a computer doesn't really know what a photo of a dog is. 01:36.980 --> 01:39.960 The only thing it understands is zeros and ones. 01:39.980 --> 01:41.570 So a lot of photos. 01:41.570 --> 01:49.520 For example, let's say we had a very simple photograph of a giant X, maybe this letter x. 01:49.940 --> 01:57.170 Well, a computer can understand an image based on pixels on the screen, so maybe we can have zero, 01:57.260 --> 01:59.690 one, zero. 02:01.130 --> 02:09.140 100 or sorry, one here, zero here, and then one. 02:09.590 --> 02:12.290 And right now, a computer can look at this. 02:12.290 --> 02:19.400 And if this represented, let's say, a tiny little pixel here or maybe a pixel here on my screen, 02:19.580 --> 02:22.640 the computer is going to say, oh, there's a one here. 02:22.640 --> 02:30.560 So that means I should make this green in this corner, then dark here, then green, then dark green, 02:30.560 --> 02:32.810 dark green, dark green. 02:32.990 --> 02:37.070 And a computer is able to draw, let's say, an X. 02:37.400 --> 02:39.620 And this is a simple example. 02:39.620 --> 02:44.360 And using matrices, we can do a lot of these heavy calculations. 02:44.360 --> 02:49.430 And that's how computers work underneath the hood when, let's say, for example, it's trying to display 02:49.430 --> 02:50.060 something. 02:50.060 --> 02:58.400 But the reason I wanted to talk about this here is when you want to access a multi dimensional list, 02:58.460 --> 03:02.600 well, you would do something like this, let's say matrix. 03:04.080 --> 03:06.900 Access the first item. 03:07.820 --> 03:14.600 In The Matrix, which in this case will be this first array because it's the first item. 03:14.600 --> 03:19.640 And then let's say we want to access the zero in here or let's change this to five. 03:19.850 --> 03:24.230 Well, I'll do square brackets again and just do zero one. 03:24.230 --> 03:25.280 So if I go. 03:26.660 --> 03:28.730 One here, and let's print that out. 03:33.640 --> 03:34.750 And I click Run. 03:36.570 --> 03:37.760 I get five. 03:37.770 --> 03:40.380 So it's accessing the first item in the array. 03:40.380 --> 03:46.500 So it's going to look at the first order array, grab the first item which is right here, and then 03:46.500 --> 03:49.200 grab the second item in that array. 03:49.200 --> 03:52.050 So zero one, which is five. 03:53.060 --> 03:54.500 And you can keep doing this. 03:54.500 --> 03:59.270 If he had multi dimensional arrays, you can keep adding, keep adding, keep adding. 04:00.360 --> 04:04.610 To access that information from an array or list. 04:04.620 --> 04:08.070 But remember in Python, we want to use the term list. 04:08.730 --> 04:09.810 I'll see you in the next one. 04:10.080 --> 04:10.710 Bye bye.