1 00:00:06,460 --> 00:00:07,810 In this video. 2 00:00:07,840 --> 00:00:14,740 Let's continue our array methods and we are going to talk about filter method. 3 00:00:14,920 --> 00:00:22,780 Well, filter method is one of my favorite methods when it comes to array because with this method we 4 00:00:22,780 --> 00:00:27,490 can achieve a complex logic with few lines of code. 5 00:00:27,520 --> 00:00:33,650 So let's say that we have a list of students, so let's bring back our students array here. 6 00:00:33,670 --> 00:00:35,380 Think it's going fast. 7 00:00:35,380 --> 00:00:41,620 So let me copy here and comment this one out and now let's bring it inside the filter method. 8 00:00:42,370 --> 00:00:48,040 So for these students, let's say that we want to know which student owes the school. 9 00:00:48,070 --> 00:00:56,230 Maybe you have a debit to be paid so we can use filter to filter out all those students who are owing 10 00:00:56,230 --> 00:00:56,980 the school. 11 00:00:57,340 --> 00:00:58,780 So in that case. 12 00:01:00,010 --> 00:01:05,620 So in this case, let's add additional property code debt, meaning you are owing the school. 13 00:01:05,740 --> 00:01:09,460 So let's say that the first student indeed you are in the school. 14 00:01:09,490 --> 00:01:17,200 So here we can copy this one and paste it here and then paste it here and also paste it here. 15 00:01:17,560 --> 00:01:19,020 The first one is Mary. 16 00:01:19,030 --> 00:01:22,630 Listen, that Mary is not in the school, so it's going to be first. 17 00:01:22,750 --> 00:01:24,440 Likewise, Sally. 18 00:01:24,460 --> 00:01:28,690 So Sally also is not only in the school, so forth. 19 00:01:28,810 --> 00:01:35,440 So for this kind of record, because we have few data here, when I ask you that, please, can you 20 00:01:35,440 --> 00:01:42,070 print out all those students who are not owing the school because we have only four records? 21 00:01:42,100 --> 00:01:44,300 You can say, yes, this is pretty easy. 22 00:01:44,320 --> 00:01:45,220 I'll look through. 23 00:01:45,220 --> 00:01:50,410 The first one is Mary, depth is first and then Sally also depth is false here. 24 00:01:50,410 --> 00:01:54,610 So it means that Mary and Sally are not all in the school. 25 00:01:55,090 --> 00:01:57,970 So I can just print out those names easily. 26 00:01:58,480 --> 00:02:00,610 So what about if you have a bunch of students? 27 00:02:00,610 --> 00:02:02,090 How are you going to do it? 28 00:02:02,110 --> 00:02:04,690 That's why Filter comes into play. 29 00:02:04,720 --> 00:02:08,830 So with Filter, we can do a lot of logic inside our code. 30 00:02:08,830 --> 00:02:16,000 For example, we can calculate which student age is more than 20 years or which students age is less 31 00:02:16,000 --> 00:02:17,080 than 23 years. 32 00:02:17,200 --> 00:02:21,210 So because of filter, we can achieve this one with few lines of code. 33 00:02:21,220 --> 00:02:24,820 So let's see the same syntax for all the array. 34 00:02:24,830 --> 00:02:33,070 So students do not filter and all these are high order function so we can pass a callback function as 35 00:02:33,070 --> 00:02:33,550 that. 36 00:02:33,670 --> 00:02:37,480 So for this one is also take in all three arguments. 37 00:02:37,480 --> 00:02:40,390 But what we came with here is an actual student. 38 00:02:40,390 --> 00:02:44,350 So here my error function and there we go. 39 00:02:44,680 --> 00:02:51,430 So for this one, we have access to the individual student as STD or student for short. 40 00:02:52,000 --> 00:02:57,040 So for this one filter also create new array as map. 41 00:02:57,280 --> 00:03:02,620 But with filter we can mix some logic before returning it, unlike map. 42 00:03:02,800 --> 00:03:04,240 So we see differences now. 43 00:03:04,240 --> 00:03:10,510 So let's check it out and see how can we retain all students who are all in the school? 44 00:03:10,810 --> 00:03:11,380 Perfect. 45 00:03:11,380 --> 00:03:14,200 So for this implementation, here we go. 46 00:03:14,230 --> 00:03:15,310 It's pretty simple, right? 47 00:03:15,310 --> 00:03:17,530 So you bring in return. 48 00:03:18,190 --> 00:03:20,920 And for return we have the student. 49 00:03:20,920 --> 00:03:23,920 This one, there is nothing new until this point. 50 00:03:24,250 --> 00:03:28,030 So let's assign a value core. 51 00:03:28,270 --> 00:03:33,190 Let me say student new student let me say dead. 52 00:03:33,190 --> 00:03:35,620 Student Then you put in that way. 53 00:03:36,730 --> 00:03:38,590 Okay, so equal to that. 54 00:03:38,590 --> 00:03:47,110 So if I console.log the dead student, meaning those who are only school, if I console.log quizzes 55 00:03:47,110 --> 00:03:51,100 that I see all the false students being displayed. 56 00:03:51,100 --> 00:03:54,970 Whether you are own or not, your name is still here. 57 00:03:55,060 --> 00:04:02,640 So the cool thing about Filter is that we can implement our own logic before returning the data. 58 00:04:02,650 --> 00:04:13,000 So what I'm going to do is that if student dot depth is equal to true meaning, those students are own. 59 00:04:13,000 --> 00:04:15,190 So when I save it, let's see. 60 00:04:15,190 --> 00:04:21,959 I'm going to have two students only instead of four, because these two students are having depth. 61 00:04:21,970 --> 00:04:25,360 That is why we see depth depth here, which is equal to true. 62 00:04:26,140 --> 00:04:33,580 So now let's say that if you change all this one to force, it means that no student is worth over in 63 00:04:33,580 --> 00:04:34,120 the school. 64 00:04:34,150 --> 00:04:41,020 So let's see, you're going to have empty array because for this one, there is no student who is or 65 00:04:41,020 --> 00:04:42,610 who owned the school. 66 00:04:42,850 --> 00:04:45,820 So let's bring back two students in the mix. 67 00:04:45,820 --> 00:04:48,460 So these two students are already in the school. 68 00:04:48,490 --> 00:04:52,980 So you can see that now we have two students in the array as that. 69 00:04:52,980 --> 00:04:55,600 That's a beauty about water. 70 00:04:55,630 --> 00:05:01,810 So we can also calculate which student age is more than 20 years or 30 years. 71 00:05:01,840 --> 00:05:04,000 I think you can try this on your own. 72 00:05:04,150 --> 00:05:09,670 So for this particular syntax tool, we can simplify it because we are using a function. 73 00:05:09,850 --> 00:05:16,090 So because we are just retaining a statement, we can even ignore the codebases and remove this one 74 00:05:16,090 --> 00:05:20,800 and remove the return statement and I remove this one. 75 00:05:20,920 --> 00:05:25,150 And when I save it, yes, this is perfect syntax for error function. 76 00:05:25,150 --> 00:05:30,790 So if this function is to confuse this, you stick to normal function like this one and you'll be good 77 00:05:30,790 --> 00:05:32,380 to go the same process. 78 00:05:32,380 --> 00:05:37,210 So what about, like I said, let's find all students whose names is John. 79 00:05:37,210 --> 00:05:38,140 We can do it. 80 00:05:38,140 --> 00:05:41,350 What about our students whose age is less than 20 years? 81 00:05:41,350 --> 00:05:43,270 So we can do that quickly. 82 00:05:43,270 --> 00:05:52,180 So here, just bring in the here and let's see the age, which is less than 20. 83 00:05:52,180 --> 00:05:55,120 Let's see, 30 years if I save it. 84 00:05:55,120 --> 00:05:55,840 Let's see. 85 00:05:55,840 --> 00:05:57,670 We have all the four students. 86 00:05:57,670 --> 00:05:59,410 Because all the four students. 87 00:05:59,520 --> 00:06:01,690 Age less than 30 years. 88 00:06:01,710 --> 00:06:09,640 So what about if you make use of less than 26 years old? 89 00:06:09,660 --> 00:06:16,470 Let's say you're going to have three students because looking at their ages, 20, 22 and 23 are less 90 00:06:16,470 --> 00:06:17,190 than 30. 91 00:06:17,190 --> 00:06:17,760 26. 92 00:06:17,760 --> 00:06:20,820 Yes, that is it about theater. 93 00:06:21,480 --> 00:06:23,820 Again, you are going to make use of this a lot. 94 00:06:23,820 --> 00:06:30,750 So let's go rockin the next video and talk about another important method called Reduced.