WEBVTT 1 00:00:00.370 --> 00:00:01.750 Hi Guys, and welcome back. 2 00:00:01.750 --> 00:00:04.690 In this video, we're going to learn how to draw bar charts. 3 00:00:04.690 --> 00:00:08.070 And we're going to use a polling data as a source of data. 4 00:00:08.070 --> 00:00:09.483 So let's get started. 5 00:00:10.380 --> 00:00:11.920 When we were drawing a pie chart, 6 00:00:11.920 --> 00:00:14.010 we plotted option texts 7 00:00:14.010 --> 00:00:16.050 against the sum of their votes 8 00:00:16.050 --> 00:00:19.360 so that we can create a pie chart for each poll. 9 00:00:19.360 --> 00:00:22.010 Now, we're going to be blocking every poll 10 00:00:22.010 --> 00:00:24.910 together with the total number of votes in that poll 11 00:00:24.910 --> 00:00:28.060 as a bar chart, so we have to change this query slightly 12 00:00:28.060 --> 00:00:33.060 to give us the poll name and the sum of votes. 13 00:00:33.260 --> 00:00:38.260 So we're going to select polls.title and the sum of votes. 14 00:00:39.550 --> 00:00:42.699 But now of course, we want to select from polls, 15 00:00:42.699 --> 00:00:45.083 we wanna join options. 16 00:00:46.310 --> 00:00:49.500 And down here, we're not going to set a where 17 00:00:49.500 --> 00:00:53.600 and we're gonna group by polls.name. 18 00:00:53.600 --> 00:00:56.260 Of course, we now have to change the name of our query 19 00:00:56.260 --> 00:00:59.550 to select polls and votes 20 00:00:59.550 --> 00:01:01.980 and we no longer need this query up here. 21 00:01:01.980 --> 00:01:03.850 So we're gonna get rid of that 22 00:01:03.850 --> 00:01:07.130 and just get this one there. 23 00:01:07.130 --> 00:01:09.530 Now we can go back to app.py 24 00:01:09.530 --> 00:01:11.620 and see what we need to change in here, 25 00:01:11.620 --> 00:01:13.237 our user input is going to change slightly. 26 00:01:13.237 --> 00:01:15.880 In fact, we don't have any user input anymore. 27 00:01:15.880 --> 00:01:18.810 All that we have is the creation of the graph. 28 00:01:18.810 --> 00:01:21.960 We don't need the user to tell us any information. 29 00:01:21.960 --> 00:01:23.142 So all that we'll do here 30 00:01:23.142 --> 00:01:25.084 is we're gonna get rid of everything. 31 00:01:25.084 --> 00:01:30.084 And just do charts.create bar chart 32 00:01:31.160 --> 00:01:34.280 with the database.get options. 33 00:01:34.280 --> 00:01:36.670 And of course, that does have to get renamed as well 34 00:01:36.670 --> 00:01:39.120 get polls and votes, there we go. 35 00:01:39.120 --> 00:01:41.680 That's a better function naming database.py 36 00:01:41.680 --> 00:01:42.840 we'll use that here. 37 00:01:42.840 --> 00:01:46.620 Once we've created the bar chart, we can do plt.show 38 00:01:46.620 --> 00:01:48.050 in order to display it. 39 00:01:48.050 --> 00:01:52.210 And now we can go into charts.py and add this function. 40 00:01:52.210 --> 00:01:56.410 So we'll go to charts.py, and we're gonna do this 41 00:01:56.410 --> 00:01:59.670 we're gonna get the poll information in here 42 00:01:59.670 --> 00:02:02.100 and we're gonna figure out how to create our bar chart, 43 00:02:02.100 --> 00:02:04.560 the first thing though, is to create the figure. 44 00:02:04.560 --> 00:02:07.590 So we do figure=plt.figure. 45 00:02:07.590 --> 00:02:11.830 Then we'll create our axes figure.addsubplots one, one, one. 46 00:02:11.830 --> 00:02:13.850 Notice that here we're creating two different figures. 47 00:02:13.850 --> 00:02:16.810 So it's okay to use the same coordinates for the subplot. 48 00:02:16.810 --> 00:02:18.490 In fact, that's what you should do. 49 00:02:18.490 --> 00:02:20.310 Because these will not overlap. 50 00:02:20.310 --> 00:02:23.100 They are on different canvases all together. 51 00:02:23.100 --> 00:02:25.090 Then at the end, we're gonna return figure. 52 00:02:25.090 --> 00:02:28.030 And here in the middle, we're going to draw our bar chart, 53 00:02:28.030 --> 00:02:30.530 which is axes.bar. 54 00:02:30.530 --> 00:02:32.800 Now, what do we put in there, 55 00:02:32.800 --> 00:02:36.640 we need the coordinates of each bar in the x axis. 56 00:02:36.640 --> 00:02:40.180 So that's zero, one, two, three, and so on. 57 00:02:40.180 --> 00:02:42.750 And we also need the heights of the bars. 58 00:02:42.750 --> 00:02:45.870 So here we're gonna pass in the coordinates of each bar, 59 00:02:45.870 --> 00:02:48.910 we're gonna do that with range of Len of polls, 60 00:02:48.910 --> 00:02:50.630 that is going to give us essentially, 61 00:02:50.630 --> 00:02:51.643 I'm sorry, that should be polls there, 62 00:02:51.643 --> 00:02:54.090 that that is going to give us an iterable 63 00:02:54.090 --> 00:02:56.430 that contains the numbers between zero 64 00:02:56.430 --> 00:02:58.030 and the length of polls. 65 00:02:58.030 --> 00:03:00.350 So it's gonna go, if we have 10 polls for example, 66 00:03:00.350 --> 00:03:03.930 from zero to nine, giving us 10 different coordinates 67 00:03:03.930 --> 00:03:04.990 zero, one, two, three, four, 68 00:03:04.990 --> 00:03:06.464 five, six, seven, eight, nine. 69 00:03:06.464 --> 00:03:08.990 So this is the first argument to the bar method. 70 00:03:08.990 --> 00:03:12.360 The second one is the heights of each column. 71 00:03:12.360 --> 00:03:17.360 So we're going to do poll one for poll in polls. 72 00:03:17.940 --> 00:03:21.370 And that is going to give us the heights. 73 00:03:21.370 --> 00:03:23.680 Okay, this is actually probably enough. 74 00:03:23.680 --> 00:03:26.833 So let's go back to app.py and run this. 75 00:03:29.620 --> 00:03:31.200 We actually made a small mistake here. 76 00:03:31.200 --> 00:03:34.750 We don't need a argument in here anymore. 77 00:03:34.750 --> 00:03:37.110 So I did forget to get rid of this. 78 00:03:37.110 --> 00:03:38.580 We don't need any of that anymore. 79 00:03:38.580 --> 00:03:39.830 So, sorry about that, 80 00:03:39.830 --> 00:03:41.380 let's go back and run it again. 81 00:03:42.320 --> 00:03:43.830 And another small mistake here 82 00:03:43.830 --> 00:03:46.720 back into database.py we need to group by title 83 00:03:46.720 --> 00:03:48.963 since that is the name of our column. 84 00:03:49.866 --> 00:03:51.060 Running that again, 85 00:03:51.060 --> 00:03:53.010 we get now our polls 86 00:03:53.010 --> 00:03:56.840 notice that each poll has a different number of votes in it. 87 00:03:56.840 --> 00:03:59.780 And this is a distribution of our votes. 88 00:03:59.780 --> 00:04:03.600 This is cool, but we can't see which poll the votes are for. 89 00:04:03.600 --> 00:04:07.060 So let's fix that by going over to charts.py, 90 00:04:07.060 --> 00:04:08.660 we're going to add a couple of things here. 91 00:04:08.660 --> 00:04:09.890 I'm going to start off by closing 92 00:04:09.890 --> 00:04:11.450 the project on the left though, 93 00:04:11.450 --> 00:04:13.540 since we don't really need that. 94 00:04:13.540 --> 00:04:15.070 In order to display a label, 95 00:04:15.070 --> 00:04:17.860 we need to pass in another argument tick label. 96 00:04:17.860 --> 00:04:21.790 And this has to contain a string for each column. 97 00:04:21.790 --> 00:04:25.380 So we'll do poll zero for poll, in polls 98 00:04:25.380 --> 00:04:27.410 and that is going to give us one string 99 00:04:27.410 --> 00:04:29.023 for each column that we've created. 100 00:04:29.023 --> 00:04:32.190 Now rerunning this is going to give us 101 00:04:32.190 --> 00:04:33.780 the poll titles there, 102 00:04:33.780 --> 00:04:36.690 but as you can see, not terribly easy to see, 103 00:04:36.690 --> 00:04:38.270 especially because they are long. 104 00:04:38.270 --> 00:04:39.500 So there's a few things we can do, 105 00:04:39.500 --> 00:04:41.110 we can obviously extend this 106 00:04:41.110 --> 00:04:44.280 until you can barely see them in this big screen, 107 00:04:44.280 --> 00:04:45.712 and not ideal. 108 00:04:45.712 --> 00:04:48.462 I'm sure there's something that we can do a bit better. 109 00:04:49.530 --> 00:04:51.440 The usual thing to do with these labels 110 00:04:51.440 --> 00:04:53.530 is to rotate them slightly 111 00:04:53.530 --> 00:04:57.520 so that they'll appear, you know, like this in each side, 112 00:04:57.520 --> 00:04:59.510 rather than straight and that way 113 00:04:59.510 --> 00:05:01.440 because they'll all be slightly rotated, 114 00:05:01.440 --> 00:05:03.610 they won't intersect with each other. 115 00:05:03.610 --> 00:05:05.036 However, in order to do that, 116 00:05:05.036 --> 00:05:08.990 we also need to make this area down here a little bit bigger 117 00:05:08.990 --> 00:05:11.770 so that they'll have more space when they are rotated. 118 00:05:11.770 --> 00:05:13.520 Otherwise they will end up clipped. 119 00:05:14.390 --> 00:05:15.670 So let's learn in the next video 120 00:05:15.670 --> 00:05:17.640 how to adjust this area down here, 121 00:05:17.640 --> 00:05:19.460 how to adjust the size of the plot. 122 00:05:19.460 --> 00:05:21.030 And then in the video after that, 123 00:05:21.030 --> 00:05:23.320 we'll learn how to rotate our labels. 124 00:05:23.320 --> 00:05:24.870 I'll see you in the next video.