1 00:00:01,440 --> 00:00:04,520 Welcome to Coding Challenge number three. 2 00:00:04,520 --> 00:00:07,293 And this is gonna be a quick and easy one. 3 00:00:09,260 --> 00:00:12,130 So all I want you to do is to rewrite 4 00:00:12,130 --> 00:00:14,906 the 'calcAverageHumanAge' function 5 00:00:14,906 --> 00:00:17,870 that we wrote in the previous challenge. 6 00:00:17,870 --> 00:00:20,500 Now the difference here is that this time, 7 00:00:20,500 --> 00:00:22,530 you should use an arrow function 8 00:00:22,530 --> 00:00:25,140 and you should use chaining. 9 00:00:25,140 --> 00:00:27,170 Now to make this chaining work, 10 00:00:27,170 --> 00:00:29,700 just keep in mind the second way that I used 11 00:00:29,700 --> 00:00:32,970 in the last challenge to calculate the average. 12 00:00:32,970 --> 00:00:35,710 Then, as always, use this test data here 13 00:00:35,710 --> 00:00:38,090 to try out your function. 14 00:00:38,090 --> 00:00:40,010 And so I'll see you here in a minute, 15 00:00:40,010 --> 00:00:42,793 or five minutes maybe, once you're done. 16 00:00:46,030 --> 00:00:48,890 Now all right, so let's grab the code here 17 00:00:48,890 --> 00:00:50,313 from the previous one. 18 00:00:51,960 --> 00:00:54,953 So there's no need to just rewrite everything. 19 00:00:58,320 --> 00:01:00,800 So let's get rid of all the comments here, 20 00:01:00,800 --> 00:01:02,273 all the console.logs. 21 00:01:03,910 --> 00:01:05,970 And so let's save it here, 22 00:01:05,970 --> 00:01:08,623 and then rewrite it as an arrow function. 23 00:01:13,000 --> 00:01:14,963 So it still takes in the ages, 24 00:01:16,370 --> 00:01:20,240 and now what it returns is simply the ages, 25 00:01:20,240 --> 00:01:22,053 then dot, this map, 26 00:01:23,370 --> 00:01:25,703 so calculating the human ages. 27 00:01:26,790 --> 00:01:29,810 Okay, and then on the result of that, 28 00:01:29,810 --> 00:01:33,930 we filter for only the adult docs. 29 00:01:33,930 --> 00:01:36,253 So when the age is greater than 18. 30 00:01:37,130 --> 00:01:39,003 So this is what we have for now. 31 00:01:40,040 --> 00:01:41,753 Let's call this one here two. 32 00:01:43,550 --> 00:01:48,130 Okay. And so for now this is the two erase that we have 33 00:01:48,130 --> 00:01:49,940 one for each function call. 34 00:01:49,940 --> 00:01:53,740 But now let's then also calculate the average. 35 00:01:53,740 --> 00:01:56,770 And so for that all we need to do is to chain 36 00:01:56,770 --> 00:01:59,580 this method of calculating the average. 37 00:01:59,580 --> 00:02:01,740 That he showed you in the last lecture, 38 00:02:01,740 --> 00:02:03,440 or actually in the last challenge. 39 00:02:04,780 --> 00:02:06,473 So pasting that here. 40 00:02:07,520 --> 00:02:11,300 And so now we get the exact same results as before, 41 00:02:11,300 --> 00:02:13,660 and that's actually already it. 42 00:02:13,660 --> 00:02:15,950 Now what's really important to notice here, 43 00:02:15,950 --> 00:02:19,820 is that this is actually really the only way 44 00:02:19,820 --> 00:02:22,300 of calculating the average now. 45 00:02:22,300 --> 00:02:25,180 So basically dividing the age by the length 46 00:02:25,180 --> 00:02:27,930 of the current array immediately here 47 00:02:27,930 --> 00:02:30,120 in each of the iteration. 48 00:02:30,120 --> 00:02:32,400 So remember that in the last challenge, 49 00:02:32,400 --> 00:02:35,380 I first simply added all the values together. 50 00:02:35,380 --> 00:02:39,580 And then afterwards I divided it by the length of the array. 51 00:02:39,580 --> 00:02:42,760 So in this case, by the length of the adults array. 52 00:02:42,760 --> 00:02:45,660 However, that would not work in this case. 53 00:02:45,660 --> 00:02:48,620 Because there would be no way of knowing the length 54 00:02:48,620 --> 00:02:50,300 of the adults array. 55 00:02:50,300 --> 00:02:53,100 So of this result here, right? 56 00:02:53,100 --> 00:02:55,180 Because we haven't stored it anyway. 57 00:02:55,180 --> 00:03:00,180 And so we couldn't do like this, like adults.length, right? 58 00:03:01,990 --> 00:03:03,340 This wouldn't be possible 59 00:03:03,340 --> 00:03:07,090 because adults here does not exist anywhere. 60 00:03:07,090 --> 00:03:09,930 And therefore we need to take that length 61 00:03:09,930 --> 00:03:12,120 from this input here. 62 00:03:12,120 --> 00:03:14,050 So from this fourth parameter, 63 00:03:14,050 --> 00:03:16,010 which gives us access to the array, 64 00:03:16,010 --> 00:03:18,770 on which the method is called. 65 00:03:18,770 --> 00:03:21,390 And that's the reason why I showed you this way here, 66 00:03:21,390 --> 00:03:22,870 in the last lecture. 67 00:03:22,870 --> 00:03:25,680 Because yeah, again this is the only way 68 00:03:25,680 --> 00:03:29,140 in which we can now calculate this average, 69 00:03:29,140 --> 00:03:31,470 unless we wanted to do it in two steps. 70 00:03:31,470 --> 00:03:32,770 But my instruction here 71 00:03:32,770 --> 00:03:35,930 was to really do it all with chaining. 72 00:03:35,930 --> 00:03:37,913 And so this is the way to go then. 73 00:03:39,330 --> 00:03:41,590 All right, so make sure you understand 74 00:03:41,590 --> 00:03:45,000 really why and also how this one here works. 75 00:03:45,000 --> 00:03:48,186 And then let's already move on to our next method, 76 00:03:48,186 --> 00:03:51,020 which is gonna be defined method. 77 00:03:51,020 --> 00:03:52,780 So another really cool one. 78 00:03:52,780 --> 00:03:54,623 So I can't wait to see you there.