WEBVTT 1 00:00:00.000 --> 00:00:01.010 Welcome back. 2 00:00:01.010 --> 00:00:02.100 line:15% In this video, we're going to look 3 00:00:02.100 --> 00:00:04.240 line:15% at some advanced set operations, 4 00:00:04.240 --> 00:00:09.240 which is why sets are useful compared to lists and tuples. 5 00:00:09.260 --> 00:00:11.400 So what I've got here is my art_friends 6 00:00:11.400 --> 00:00:12.640 and my science_friends. 7 00:00:12.640 --> 00:00:16.000 In arts, we've got Rolf, Anne and Jen. 8 00:00:16.000 --> 00:00:18.140 And in science, we've got Jen and Charlie. 9 00:00:18.140 --> 00:00:21.400 So a couple of things you can notice about these sets 10 00:00:21.400 --> 00:00:25.260 is that Jen does both art and science, right? 11 00:00:25.260 --> 00:00:26.780 She's in both sets. 12 00:00:26.780 --> 00:00:30.040 Rolf and Anne do art but not science. 13 00:00:30.040 --> 00:00:32.890 And Charlie does science but not art. 14 00:00:32.890 --> 00:00:34.880 And in total, we have four people, 15 00:00:34.880 --> 00:00:37.863 Rolf, Anne, Jen and Charlie. 16 00:00:38.790 --> 00:00:42.100 So we can use sets to extract that information 17 00:00:42.100 --> 00:00:43.770 from this data. 18 00:00:43.770 --> 00:00:44.860 Here's how. 19 00:00:44.860 --> 00:00:48.193 Let's get those people that do art but not science. 20 00:00:48.193 --> 00:00:50.987 So we'll say art_but_not_science. 21 00:00:50.987 --> 00:00:52.016 And what you want to do 22 00:00:52.016 --> 00:00:56.965 is you wanna say art_friends.difference(science_friends). 23 00:00:56.965 --> 00:00:59.530 So the difference gives you which elements 24 00:00:59.530 --> 00:01:02.773 are in art that are not in science. 25 00:01:02.773 --> 00:01:06.830 So the ones that are in art but not in science 26 00:01:06.830 --> 00:01:09.820 means that it's gonna do Rolf, Anne and Jen, 27 00:01:09.820 --> 00:01:12.970 it's gonna take away all the elements that are here 28 00:01:12.970 --> 00:01:13.920 that are also here. 29 00:01:13.920 --> 00:01:17.370 So in this case, Jen is both, so it's gonna get taken away 30 00:01:17.370 --> 00:01:19.833 and what you'll get back is Rolf and Anne. 31 00:01:21.000 --> 00:01:23.357 Of course you can do science_but_not_art 32 00:01:24.460 --> 00:01:25.880 and it's just the opposite 33 00:01:25.880 --> 00:01:27.880 science_friends.difference(art_friends). 34 00:01:29.640 --> 00:01:31.010 And what that's gonna do is it's gonna take 35 00:01:31.010 --> 00:01:32.870 your science friends, Jen and Charlie 36 00:01:32.870 --> 00:01:36.880 and it's gonna take away those that are in art, so Jen. 37 00:01:36.880 --> 00:01:39.640 And it's gonna leave you just with Charlie. 38 00:01:39.640 --> 00:01:40.740 Let's print those out. 39 00:01:42.210 --> 00:01:43.560 And you'll see what I mean. 40 00:01:44.520 --> 00:01:47.260 So in the first one you have Anne and Rolf 41 00:01:47.260 --> 00:01:48.520 but not Jen. 42 00:01:48.520 --> 00:01:51.510 And in the second one you have Charlie but not Jen. 43 00:01:51.510 --> 00:01:52.960 Sometimes what you want is something 44 00:01:52.960 --> 00:01:55.100 called the symmetric difference, 45 00:01:55.100 --> 00:01:58.920 which is members that aren't in both sets. 46 00:01:58.920 --> 00:02:02.380 So what members are not in both sets? 47 00:02:02.380 --> 00:02:04.213 Rolf, Anne and Charlie. 48 00:02:05.110 --> 00:02:07.190 So let's get that. 49 00:02:07.190 --> 00:02:09.240 So not_in_both 50 00:02:09.240 --> 00:02:12.567 will be art_friends.symmetric_difference(science_friends). 51 00:02:17.780 --> 00:02:20.350 So you get Anne, Rolf and Charlie. 52 00:02:20.350 --> 00:02:23.720 So those are the members that are not in both. 53 00:02:23.720 --> 00:02:26.090 Since Jen is the only one that's in both, 54 00:02:26.090 --> 00:02:28.890 what you end up is everything together 55 00:02:28.890 --> 00:02:31.510 except the ones that are in both. 56 00:02:31.510 --> 00:02:33.630 Of course because it says symmetric difference, 57 00:02:33.630 --> 00:02:35.610 it doesn't matter which one goes first. 58 00:02:35.610 --> 00:02:36.621 You can put 59 00:02:36.621 --> 00:02:38.620 science_friends.symmetric_difference, art_friends 60 00:02:38.620 --> 00:02:40.155 or you can do what we've done here, 61 00:02:40.155 --> 00:02:43.280 art_friends.symmetric_difference(science_friends). 62 00:02:43.280 --> 00:02:46.090 So to recap, difference does elements 63 00:02:46.090 --> 00:02:48.400 that are in one but not the other, 64 00:02:48.400 --> 00:02:50.380 where the symmetric difference does elements 65 00:02:50.380 --> 00:02:52.200 that are not in both. 66 00:02:52.200 --> 00:02:55.320 If you wanted the members that are in both sets, 67 00:02:55.320 --> 00:02:57.850 so Jen, you can do that 68 00:02:57.850 --> 00:02:59.490 with something called the intersection. 69 00:02:59.490 --> 00:03:02.020 So you could do who is doing art and science, 70 00:03:02.020 --> 00:03:07.020 art_and_science and that would be art_friends.intersection 71 00:03:07.520 --> 00:03:09.217 with science_friends. 72 00:03:10.860 --> 00:03:14.800 And what that would give you is just Jen in her own set. 73 00:03:14.800 --> 00:03:16.720 Notice that this is still a set 74 00:03:16.720 --> 00:03:19.100 because it has the curly braces around it. 75 00:03:19.100 --> 00:03:21.453 So that is a set of one element. 76 00:03:22.930 --> 00:03:25.120 Finally, if you wanted all the people 77 00:03:25.120 --> 00:03:28.820 that are studying any subject, but without duplicates, 78 00:03:28.820 --> 00:03:33.820 you could do all_friends is art_friends.union 79 00:03:34.430 --> 00:03:36.080 with science_friends. 80 00:03:36.080 --> 00:03:38.140 And that is gonna unite both sets 81 00:03:38.140 --> 00:03:40.793 and give you one big set with everybody in it. 82 00:03:42.300 --> 00:03:44.730 Of course, note that Jen is there twice, 83 00:03:44.730 --> 00:03:48.020 so it's only gonna appear once in the final set 84 00:03:48.020 --> 00:03:49.870 because sets cannot contain duplicates 85 00:03:49.870 --> 00:03:51.740 and you can see that this is still a set 86 00:03:51.740 --> 00:03:53.390 so there are no duplicates in it. 87 00:03:54.500 --> 00:03:58.550 These operations are why sets are useful. 88 00:03:58.550 --> 00:04:02.540 For example, you could have a lottery game 89 00:04:02.540 --> 00:04:05.160 where your user has a few numbers 90 00:04:05.160 --> 00:04:08.150 and the system has decided on six numbers 91 00:04:08.150 --> 00:04:10.570 that are the lottery winners. 92 00:04:10.570 --> 00:04:13.620 By having them both on sets, you could calculate 93 00:04:13.620 --> 00:04:15.000 the intersection of them two, 94 00:04:15.000 --> 00:04:16.710 which elements the user has matched 95 00:04:16.710 --> 00:04:18.850 with the winning elements 96 00:04:18.850 --> 00:04:21.520 and then calculate the user's winnings like that. 97 00:04:21.520 --> 00:04:23.950 And that is, in fact, going to be one of the challenges 98 00:04:23.950 --> 00:04:25.540 for this section. 99 00:04:25.540 --> 00:04:28.050 If you're not completely sure when to use 100 00:04:28.050 --> 00:04:31.820 each of these data structures, lists, tuples and sets, 101 00:04:31.820 --> 00:04:33.130 don't worry too much, 102 00:04:33.130 --> 00:04:35.310 over time you will get better at it. 103 00:04:35.310 --> 00:04:39.120 And most of the time, you'll be using tuples and lists. 104 00:04:39.120 --> 00:04:42.793 Sets are reserved for when you want to use these operations. 105 00:04:43.700 --> 00:04:45.000 Thanks for joining me in this video, 106 00:04:45.000 --> 00:04:46.060 I hope you've learned something, 107 00:04:46.060 --> 00:04:47.613 line:15% and I'll see you in the next one.