WEBVTT 1 00:00:01.184 --> 00:00:03.963 (Instructor)This is coding challenge number two. 2 00:00:05.530 --> 00:00:06.363 And in this one, 3 00:00:06.363 --> 00:00:10.730 we're gonna go back to Julia in case study about dogs. 4 00:00:10.730 --> 00:00:14.350 And this time, they want to convert the ages of the dogs 5 00:00:14.350 --> 00:00:18.243 to human ages, and then calculate their average age. 6 00:00:19.940 --> 00:00:21.370 So your job is to create 7 00:00:21.370 --> 00:00:24.720 this calc average human age function. 8 00:00:24.720 --> 00:00:28.550 And this function accepts an array of dogs ages. 9 00:00:28.550 --> 00:00:30.963 And it does the following four tasks, 10 00:00:31.890 --> 00:00:34.160 or actually just three tasks. 11 00:00:34.160 --> 00:00:37.370 So first, calculate the age of all the dogs 12 00:00:37.370 --> 00:00:40.910 in human years using this formula. 13 00:00:40.910 --> 00:00:44.720 So if the dog is less or equal two years old, 14 00:00:44.720 --> 00:00:48.850 then the human age is simply twice the dog's age. 15 00:00:48.850 --> 00:00:51.240 But if the dog is older than two years, 16 00:00:51.240 --> 00:00:55.390 then the human age is calculated by this formula. 17 00:00:55.390 --> 00:00:56.530 All right. 18 00:00:56.530 --> 00:00:59.310 Then in the next step, exclude all the dogs 19 00:00:59.310 --> 00:01:02.710 that are less than 18 human years old. 20 00:01:02.710 --> 00:01:05.840 And that is essentially the same as keeping the dogs 21 00:01:05.840 --> 00:01:10.840 that are at least 18 years old here okay. 22 00:01:11.020 --> 00:01:12.160 Then, finally, 23 00:01:12.160 --> 00:01:16.360 calculate the average human age of all the adult dogs. 24 00:01:16.360 --> 00:01:19.660 And from the other challenges, you should already know how 25 00:01:19.660 --> 00:01:22.010 to calculate averages. 26 00:01:22.010 --> 00:01:23.320 Now, in this one, you will do it 27 00:01:23.320 --> 00:01:25.480 in a different way, hopefully, 28 00:01:25.480 --> 00:01:27.280 because the goal of this challenge 29 00:01:27.280 --> 00:01:32.010 is of course to use the Map, Filter and Reduce methods. 30 00:01:32.010 --> 00:01:34.180 Finally, then run this function 31 00:01:34.180 --> 00:01:37.290 for both these test data sets. 32 00:01:37.290 --> 00:01:41.050 So as I said, this is a way of training the map filter 33 00:01:41.050 --> 00:01:44.450 and array methods that we just studied earlier. 34 00:01:44.450 --> 00:01:46.700 And so good luck with this challenge. 35 00:01:46.700 --> 00:01:49.150 line:15% Take all the time you need and they see you here 36 00:01:49.150 --> 00:01:50.163 line:15% once you're ready. 37 00:01:53.290 --> 00:01:55.883 So were you successful in solving this one? 38 00:01:57.380 --> 00:01:59.010 I sure hope so. 39 00:01:59.010 --> 00:02:03.663 And in case there was some doubt, here is my solution. 40 00:02:06.760 --> 00:02:11.140 So this function takes an array of dog Ages. 41 00:02:11.140 --> 00:02:15.740 And then we want to convert all of these ages to human ages. 42 00:02:15.740 --> 00:02:17.480 So what we want here is to create 43 00:02:17.480 --> 00:02:20.770 a new array based on the original array. 44 00:02:20.770 --> 00:02:24.023 And so for that the map method is perfect. 45 00:02:25.700 --> 00:02:30.143 So we will have a new array called Human Ages. 46 00:02:31.750 --> 00:02:35.150 And that will be the result of calling the map method 47 00:02:35.150 --> 00:02:37.000 on the ages array. 48 00:02:37.000 --> 00:02:41.580 Then this callback function gets access to the current age, 49 00:02:41.580 --> 00:02:44.130 so the current element in the array. 50 00:02:44.130 --> 00:02:46.040 And now here what we need to return 51 00:02:46.040 --> 00:02:48.713 is the result of this formula. 52 00:02:50.660 --> 00:02:52.380 So this one here, 53 00:02:52.380 --> 00:02:55.053 and so let's write a ternary operator here. 54 00:02:56.050 --> 00:02:59.733 So if the age is less or equal two, 55 00:03:01.160 --> 00:03:06.160 then what we want to return here is two times the age, 56 00:03:06.660 --> 00:03:07.493 right? 57 00:03:07.493 --> 00:03:11.510 Because that dog age is of course, this age variable here, 58 00:03:11.510 --> 00:03:14.150 because it comes from the ages array, 59 00:03:14.150 --> 00:03:17.043 which itself is an array of dog Ages. 60 00:03:19.850 --> 00:03:23.390 Anyway, if the age is greater than two, 61 00:03:23.390 --> 00:03:28.140 then the result will be 16 plus the age times four. 62 00:03:31.380 --> 00:03:35.810 And so since this has an implicit return here, remember, 63 00:03:35.810 --> 00:03:37.743 it's like writing this here, 64 00:03:38.660 --> 00:03:39.700 okay? 65 00:03:39.700 --> 00:03:44.533 And so it's returning either this value here or actually, 66 00:03:45.910 --> 00:03:48.920 either this value, so twice the age, 67 00:03:48.920 --> 00:03:51.403 or four times the age plus 16. 68 00:03:52.860 --> 00:03:54.340 So that's the callback function, 69 00:03:54.340 --> 00:03:58.390 and this will then produce the array that we're looking for. 70 00:03:58.390 --> 00:03:59.393 Let's take a look. 71 00:04:00.290 --> 00:04:04.273 So human ages, and then we just need to call the function. 72 00:04:12.200 --> 00:04:16.500 And so here is the age converted to human ages. 73 00:04:16.500 --> 00:04:18.943 And it does indeed look correct. 74 00:04:20.520 --> 00:04:22.183 So let's assume it is correct. 75 00:04:23.610 --> 00:04:27.010 Then next up we want to filter for all the dogs 76 00:04:27.010 --> 00:04:29.920 that are at least 18 years old. 77 00:04:29.920 --> 00:04:32.270 And so that will then exclude all the dogs 78 00:04:32.270 --> 00:04:34.533 that are less than 18 years old. 79 00:04:38.320 --> 00:04:43.320 So that's gonna be the adult dogs and so that is human ages. 80 00:04:44.600 --> 00:04:49.600 And now we use the filter method and that makes sense right? 81 00:04:49.610 --> 00:04:51.980 Because it's the filter method who allows us 82 00:04:51.980 --> 00:04:55.143 to set a condition like this one. 83 00:04:56.300 --> 00:05:01.300 So when the age is at least, so great or equal 18, 84 00:05:02.380 --> 00:05:06.680 then put it in the new array which will be the adults array. 85 00:05:06.680 --> 00:05:09.490 And so let's lock that one as well. 86 00:05:09.490 --> 00:05:12.870 So actually, I want both of them here. 87 00:05:12.870 --> 00:05:14.110 So human ages 88 00:05:15.830 --> 00:05:17.763 and the adults. 89 00:05:20.100 --> 00:05:22.460 And so indeed, these two here, 90 00:05:22.460 --> 00:05:24.213 the four and the two are gone. 91 00:05:25.670 --> 00:05:26.650 Alright. 92 00:05:26.650 --> 00:05:30.220 And now finally, we want to calculate the average. 93 00:05:30.220 --> 00:05:31.053 Okay? 94 00:05:31.053 --> 00:05:33.460 And so the average is basically adding all 95 00:05:33.460 --> 00:05:35.250 of these values together, 96 00:05:35.250 --> 00:05:37.810 and then dividing the result by five, 97 00:05:37.810 --> 00:05:39.493 so the length of the array. 98 00:05:41.570 --> 00:05:44.373 So that's essentially what we already did before. 99 00:05:46.820 --> 00:05:51.543 So that's gonna be adults.reduce, 100 00:05:53.050 --> 00:05:57.210 then the accumulator and the current age. 101 00:05:57.210 --> 00:06:01.813 And we want to return the accumulator plus the age. 102 00:06:02.970 --> 00:06:05.660 And the start is gonna be at zero. 103 00:06:05.660 --> 00:06:10.010 So this here will return the sum, 104 00:06:10.010 --> 00:06:13.003 so all of these ages here added together. 105 00:06:14.220 --> 00:06:16.570 That's now all we need to do is to divide 106 00:06:16.570 --> 00:06:19.633 this by the length of this array. 107 00:06:22.307 --> 00:06:25.100 And then we simply want to return 108 00:06:25.100 --> 00:06:28.553 this average value that we just calculated. 109 00:06:29.750 --> 00:06:31.713 So let's just see if this makes sense. 110 00:06:33.270 --> 00:06:35.740 Let's actually save it here in a variable, 111 00:06:35.740 --> 00:06:38.080 instead of logging into directly. 112 00:06:38.080 --> 00:06:39.283 So average one, 113 00:06:40.970 --> 00:06:42.150 and then also 114 00:06:43.740 --> 00:06:45.333 average two. 115 00:06:56.530 --> 00:07:00.363 And then just log both here to the console. 116 00:07:02.290 --> 00:07:04.870 And all right, here they are. 117 00:07:04.870 --> 00:07:07.853 And this looks pretty reasonable to me. 118 00:07:08.830 --> 00:07:11.260 And so our solution here works. 119 00:07:11.260 --> 00:07:14.290 Now, I just wanted to let that we could have done 120 00:07:14.290 --> 00:07:17.520 this average calculation here in a different way. 121 00:07:17.520 --> 00:07:20.200 So in a bit more complex way. 122 00:07:20.200 --> 00:07:22.833 So let me show you one property of an average. 123 00:07:23.670 --> 00:07:25.860 So let's say we want to calculate the average 124 00:07:25.860 --> 00:07:28.320 of two and three. 125 00:07:28.320 --> 00:07:29.600 So we do that 126 00:07:29.600 --> 00:07:32.053 by two plus three. 127 00:07:33.920 --> 00:07:37.100 So we add all of this together and then divided by two, 128 00:07:37.100 --> 00:07:39.490 because we have two values. 129 00:07:39.490 --> 00:07:42.670 And so that is then 2.5. 130 00:07:42.670 --> 00:07:45.330 However, we can also do it in a different way. 131 00:07:45.330 --> 00:07:48.313 So we can divide both of them by two immediately. 132 00:07:49.300 --> 00:07:51.970 So two divided by two, 133 00:07:51.970 --> 00:07:54.710 plus two divided by three, 134 00:07:54.710 --> 00:07:57.510 and this will also be 2.5. 135 00:07:57.510 --> 00:08:01.440 So these here are essentially the exact same thing. 136 00:08:01.440 --> 00:08:04.653 Okay, and so here, we can do this differently. 137 00:08:05.950 --> 00:08:08.460 So let me actually duplicate this line 138 00:08:09.670 --> 00:08:11.433 So that we can keep both here. 139 00:08:13.460 --> 00:08:17.950 So what I mean is that we can actually simply divide 140 00:08:17.950 --> 00:08:20.950 the current age here immediately by the length of the array. 141 00:08:22.660 --> 00:08:23.870 Right? 142 00:08:23.870 --> 00:08:26.690 Here, this is actually three divided by two. 143 00:08:26.690 --> 00:08:29.200 Okay, sorry for that mistake. 144 00:08:29.200 --> 00:08:31.110 And so what we did here was basically 145 00:08:31.110 --> 00:08:35.650 to divide both of the values always immediately by the two. 146 00:08:35.650 --> 00:08:38.630 And so that would be the same as immediately dividing 147 00:08:38.630 --> 00:08:41.700 the age here by the length of the array. 148 00:08:41.700 --> 00:08:44.460 So dividing this by the length of the array. 149 00:08:44.460 --> 00:08:46.320 And now remember that we can get 150 00:08:46.320 --> 00:08:49.493 this length immediately here from this parameter. 151 00:08:50.590 --> 00:08:54.000 Well, not really the length, but the array itself. 152 00:08:54.000 --> 00:08:56.500 So that's the fourth parameter. 153 00:08:56.500 --> 00:09:01.240 And so now we can say array.length, like this. 154 00:09:02.490 --> 00:09:04.763 And so see what happens now here. 155 00:09:06.130 --> 00:09:09.370 And indeed, the values are exactly the same. 156 00:09:09.370 --> 00:09:11.150 And so this way of calculating it 157 00:09:11.150 --> 00:09:13.240 is just the same as this one here, 158 00:09:13.240 --> 00:09:16.260 but we can do it kind of all in one line. 159 00:09:16.260 --> 00:09:18.700 And I also wanted to show you a good use case, 160 00:09:18.700 --> 00:09:20.730 for using this array here. 161 00:09:20.730 --> 00:09:22.450 In this case, we could of course, 162 00:09:22.450 --> 00:09:26.240 also just have written here, adult.length, 163 00:09:26.240 --> 00:09:27.990 but sometimes when we change 164 00:09:27.990 --> 00:09:30.150 these methods together especially 165 00:09:30.150 --> 00:09:32.880 then this is the only way we have 166 00:09:32.880 --> 00:09:35.450 of using the current array. 167 00:09:35.450 --> 00:09:38.620 And we will see a use case of that later. 168 00:09:38.620 --> 00:09:42.080 Now of course, I did not expect you to write it like this, 169 00:09:42.080 --> 00:09:44.490 but I just wanted to show you a good use case 170 00:09:44.490 --> 00:09:48.450 for the current array parameter that we have here. 171 00:09:48.450 --> 00:09:51.570 Okay, and with that, we finish the challenge, 172 00:09:51.570 --> 00:09:53.943 and I see you in the next video.