WEBVTT 00:00.410 --> 00:00.950 Hi everyone. 00:00.950 --> 00:02.210 Welcome back to this tutorial. 00:02.210 --> 00:06.890 In this tutorial we will code and explore the grouping by collector. 00:07.280 --> 00:13.010 This is equivalent to performing a group by class in a SQL. 00:14.100 --> 00:20.310 The basic idea is that it is going to group the elements based on a property that is being passed to 00:20.310 --> 00:21.930 the group by collector. 00:22.800 --> 00:27.660 The output of the group by is always going to be a map of key value pairs. 00:28.800 --> 00:31.770 There are three different versions of grouping by. 00:32.100 --> 00:37.050 We have the one parameter version which takes in a classifier as an input. 00:37.050 --> 00:43.740 Basically that is a one which determines what is a classification value that needs to be applied to 00:43.740 --> 00:45.270 that stream input. 00:45.570 --> 00:47.430 Next is a two parameter version. 00:47.430 --> 00:52.710 The first argument is going to be a classifier, and the second argument is a downstream, which is 00:52.710 --> 00:56.730 nothing but another collector that can be of any type of collector. 00:56.730 --> 00:58.560 What were we discussing until now? 01:01.160 --> 01:06.440 The third one is the three parameter version, which takes in a classifier as a first input, and the 01:06.440 --> 01:12.710 second one is going to be a supplier which is used to override the default map factory. 01:12.710 --> 01:16.460 And then the third one is again going to be the downstream. 01:16.460 --> 01:23.420 Let's explore the one argument grouping by as part of this tutorial and then we will focus on the other 01:23.420 --> 01:26.710 group by versions in the future tutorials. 01:26.720 --> 01:28.190 Let's go ahead and code this one. 01:29.730 --> 01:31.920 Have the IntelliJ open in here. 01:31.920 --> 01:35.310 What I'm going to do, I'm going to create a class called. 01:36.560 --> 01:37.010 Green. 01:39.960 --> 01:41.850 Grouping by example. 01:43.320 --> 01:48.090 And then let's make this class executable by adding public static void main. 01:51.620 --> 01:58.010 We are going to make use of the same student database class and the use case that we are going to code. 01:58.010 --> 02:02.150 It's going to be we want to group the students based on their gender. 02:02.150 --> 02:03.140 How do we do it? 02:03.680 --> 02:05.750 Going to be public, static, void. 02:07.140 --> 02:07.590 Group. 02:09.710 --> 02:11.150 Students by. 02:12.370 --> 02:12.940 Gender. 02:13.120 --> 02:14.380 That's what we are going to do. 02:14.650 --> 02:23.200 The first call is going to be student database dot, get all students dot stream, and then we're going 02:23.200 --> 02:24.310 to call the collect method. 02:24.310 --> 02:27.190 In the collect method, we are going to make use of the. 02:28.510 --> 02:29.680 Grouping by. 02:31.750 --> 02:33.730 So let's import the static import. 02:33.910 --> 02:34.380 Here we go. 02:34.390 --> 02:34.990 You have this. 02:34.990 --> 02:37.800 Collectors are grouping by static import option available. 02:37.810 --> 02:40.120 I'm going to select that in here. 02:40.120 --> 02:43.140 If you take a look at it, there are different versions, right? 02:43.150 --> 02:47.200 What I'm going to do, the first one is going to be print, colon. 02:47.200 --> 02:47.950 Colon. 02:48.400 --> 02:50.140 Let's import the student class. 02:52.140 --> 02:53.190 Get gender. 02:54.050 --> 02:59.990 So what this is going to do, this is basically going to group the student students based on the gender. 03:00.080 --> 03:02.840 The output is going to be map of. 03:02.930 --> 03:07.490 So the gender what is the type of it is of type string, Right. 03:07.760 --> 03:14.270 So it's going to be string and it's going to give you a list of students. 03:14.270 --> 03:15.560 That's what it's going to do. 03:16.070 --> 03:17.210 List of. 03:18.890 --> 03:19.400 Goodness. 03:20.950 --> 03:23.260 And then let's import this one to. 03:25.810 --> 03:30.580 Then import the map, which is part of the Java.util package and let's give it a name. 03:30.580 --> 03:33.760 It's going to be student map. 03:35.450 --> 03:37.550 And what I'm going to do, I'm going to print it here. 03:39.830 --> 03:40.080 Map. 03:41.330 --> 03:45.470 Now the next step is we are going to make a call to this method, actually. 03:46.580 --> 03:49.130 Okay, let's run this and then check the result. 03:52.810 --> 03:53.380 So there you go. 03:53.380 --> 04:00.290 So we have the female key and male key and it has all the list of students in it. 04:00.310 --> 04:09.310 The female has Jenny, Emily and Sophia, and the male has Adam, Dave and James. 04:09.400 --> 04:14.050 So this is one way of grouping the students based on their. 04:15.400 --> 04:16.020 Gender. 04:16.030 --> 04:18.220 Now there isn't another version. 04:18.220 --> 04:22.540 So we can group by the students using some customized values. 04:22.540 --> 04:27.670 Here we have used a property, whatever that is part of the student class, right? 04:27.670 --> 04:30.940 Let's say you want to give some customized key values. 04:30.940 --> 04:37.030 It is also possible what I'm going to do, I'm going to copy this whole thing here and then I'm going 04:37.030 --> 04:39.340 to name this one as customized. 04:40.470 --> 04:41.580 Grouping by. 04:42.240 --> 04:49.530 And the use case that I'm going to code here is that I want to group the students based on their GPA. 04:49.830 --> 04:53.520 If you go here, if you go to the get all students. 04:54.650 --> 04:55.250 Method. 04:55.280 --> 04:59.420 It has all the students right from different genders. 04:59.450 --> 05:02.720 I want to categorize the students based on their GPA. 05:03.020 --> 05:07.480 If the GPA is 3.8, I want the key to be outstanding. 05:07.490 --> 05:14.960 If the GPA is less than 3.53.8, then I want them to categorize as average. 05:14.960 --> 05:16.560 So the use cases. 05:16.580 --> 05:22.190 If the GPA is greater than or equal to 3.8, 3.8, then they are outstanding students. 05:22.220 --> 05:29.330 If the GPA is less than or equal less than 3.8, then those students are going to be average students. 05:29.930 --> 05:35.900 So in the grouping by what I'm going to do, I'm going to create a lambda student. 05:37.140 --> 05:43.980 Student dot get GPA if it is greater than or equal to 3.8. 05:45.000 --> 05:50.420 And then what I'm going to do, I'm going to assign the keys. 05:51.750 --> 05:52.640 Outstanding. 05:52.650 --> 05:56.970 If not, they are going to be in the average category. 05:58.750 --> 06:04.540 Okay, What I'm going to do, I'm going to comment this one and then I'm going to make the call to this 06:04.540 --> 06:11.080 customized grouping so that it won't be confused when we are going to check the result in the console. 06:11.080 --> 06:13.270 So we are making the call to this one. 06:13.570 --> 06:15.280 Let's revisit this one again. 06:15.280 --> 06:20.230 So the student get all student method is going to return you a list of six students. 06:20.230 --> 06:25.720 And then we are calling this Stream method, which is going to create a stream of students. 06:27.020 --> 06:34.320 And then what we are doing is we are grouping the student by using a customized implementation of key. 06:34.340 --> 06:40.250 So this string is going to get outstanding or average based on their GPA. 06:40.460 --> 06:46.730 If the GPA of the student is greater than or equal to 3.8, then those students will fall and fall under 06:46.730 --> 06:48.620 the category of outstanding. 06:48.650 --> 06:52.750 Otherwise, those students will fall under the category of average. 06:52.760 --> 06:55.430 Let's run this and then check the result. 06:57.330 --> 06:58.020 There you go. 06:58.050 --> 06:59.010 It ran. 06:59.280 --> 07:02.940 The result has the average key and outstanding key. 07:02.970 --> 07:06.030 Let's review the of the students who are under the average. 07:06.030 --> 07:12.570 If you take a look at the average students, they have the 3.6 and Sofia has 3.5. 07:12.600 --> 07:20.370 So for the outstanding students, if you take a look at it, the GPA as three is 3.8 and 4.0 and 3.9 07:20.370 --> 07:21.600 and 3.9. 07:21.630 --> 07:28.620 So this is one another way of grouping the students based on your customized implementation of the grouping 07:28.620 --> 07:30.450 by implementation. 07:31.770 --> 07:33.090 This is all about the approach. 07:33.090 --> 07:38.850 One, let's discuss about the multiple level of grouping and some more advanced concepts in the future 07:38.850 --> 07:39.730 tutorials. 07:39.750 --> 07:41.940 With this, we came to the end of this tutorial. 07:41.970 --> 07:43.080 Thank you for watching.