WEBVTT 00:03.330 --> 00:05.040 Hello and welcome back to our costs. 00:05.070 --> 00:09.570 So in this session we learn about boolean indexing of some higher res. 00:09.600 --> 00:10.530 So what does it mean. 00:10.530 --> 00:17.040 So let's assume we have an umpire Ray with many elements and we want to check element y's if the element 00:17.040 --> 00:19.980 meets a certain conditions of like sample. 00:19.980 --> 00:24.480 You want to check if each element is greater than five or not. 00:24.480 --> 00:28.080 And with NUM PI we can do this in a vector rest fashion. 00:28.080 --> 00:33.210 So we do not need to write for loops or if elif and US statements. 00:33.360 --> 00:34.500 So let's start to code. 00:34.530 --> 00:35.430 Let's. 00:35.550 --> 00:36.420 Important umpire. 00:37.350 --> 00:42.750 And then we create an umpire Ray from 1 to 10 and then we check element twice. 00:42.750 --> 00:46.570 So we have a if a is greater than five. 00:46.570 --> 00:48.680 So we check for each element here. 00:48.730 --> 00:57.140 If the element is greater than five and what an umpire returns us it returns an umpire Ray with boolean 00:57.170 --> 00:58.320 objects. 00:58.330 --> 01:01.490 So here for the first elements of one is not greater than five. 01:01.490 --> 01:05.150 It gives us a false two is not greater than five false. 01:05.160 --> 01:14.090 And I can see here starting from six we get a true so an umpire returned us and boolean array on the 01:14.090 --> 01:21.520 Ravens US boolean objects and I called this a bully NRA mask ones that we see later what we can do with 01:21.520 --> 01:21.720 it. 01:23.920 --> 01:33.920 Then second we check if each element is less than eight and then we also get back in boolean array so 01:33.920 --> 01:39.870 we can see only the last three elements of our array does not fulfill the condition and gives us the 01:39.890 --> 01:46.780 false and we can also make it more complicated so we can have an and statement on and keywords here 01:47.070 --> 01:54.940 you can check which element fulfills both conditions so is greater than five and less than eight. 01:54.970 --> 02:01.520 So I would assume that the elements sixth and seventh so only two elements fulfill both conditions. 02:02.170 --> 02:04.330 So we are false false false and two times true. 02:04.330 --> 02:05.500 OK. 02:05.560 --> 02:09.640 And we can also take the R operator. 02:09.700 --> 02:12.310 So we check whether at least one condition is met. 02:12.310 --> 02:19.710 So at least the element is either greater than five or either less than eight. 02:20.410 --> 02:28.580 And this holds true for all elements so all elements at least fulfill one condition. 02:28.650 --> 02:35.820 So now what if we want the opposite of let's say our mask re so the opposite array where we have fear 02:35.880 --> 02:37.990 for each element and the opposite. 02:38.010 --> 02:46.920 Boolean value in the air we have to use the terrorism bill so this means uh not are the opposite of 02:46.920 --> 02:48.850 this expression here. 02:48.850 --> 02:49.860 So let's see what we get 02:53.190 --> 02:54.120 so let's check again. 02:54.130 --> 02:58.980 So we took you the opposite of mosque three so the opposite of forces. 02:58.980 --> 03:02.200 True False True False True. 03:02.370 --> 03:08.430 And yeah in the end so we saw here mosque three gets us to truth at Element Six and seven. 03:08.430 --> 03:13.650 And here we get truth and only two false at are the elements six and seven. 03:13.920 --> 03:15.920 And what we cannot do we cannot say. 03:16.050 --> 03:22.010 Instead of having the two the symbol become let's not say not so not does not work in an erect arised 03:22.020 --> 03:23.370 fashion. 03:23.370 --> 03:25.420 And it gives us here the value area. 03:25.530 --> 03:29.440 So the truth value of an array with more than one element is ambiguous. 03:29.520 --> 03:38.050 So not does not work in this case so we have to take here the two the symbol All right so so far we 03:38.050 --> 03:44.140 created a new and the Array method the Boolean value is that shows us whether the elements fulfilled 03:44.170 --> 03:45.760 the condition or not. 03:45.760 --> 03:51.170 And yeah what if we want to filter out the elements which fulfill that condition. 03:51.250 --> 03:54.390 So let's say here a great fire. 03:54.400 --> 03:59.470 So we want to filter out all the elements which are greater than five or six seven eight nine ten. 03:59.860 --> 04:02.000 And we can do this by brilliant indexing. 04:02.020 --> 04:04.890 So we take a and then it's paprika. 04:04.910 --> 04:09.920 We take the condition a create a five and a grade of five as a boolean in the array. 04:10.120 --> 04:12.450 Let's see what happens. 04:12.460 --> 04:21.010 So now num high returns us an array on a slice of array a we had the condition a greater than five is 04:21.010 --> 04:21.680 fulfilled. 04:21.940 --> 04:28.870 So when instead of writing here and spell brackets our condition we can just put in our mask one for 04:28.870 --> 04:31.990 example the condition of mask one is a greater five. 04:32.050 --> 04:34.310 So we already did this here. 04:34.390 --> 04:37.250 So we should get the same result. 04:37.300 --> 04:40.270 So now we want to slice a four hour mask too. 04:40.300 --> 04:43.340 So mask to what this mask to doing. 04:43.570 --> 04:46.620 The condition of mask to us all elements. 04:46.630 --> 04:50.160 Less than eight let's see. 04:52.110 --> 04:58.410 So we get all the elements until seven and mask three it should give us a six and seven. 04:58.530 --> 04:59.520 We already had that. 04:59.550 --> 05:05.410 Yes mask for should give us all elements 05:08.610 --> 05:15.450 so all elements either fulfil the condition one or condition two and mask five through should return 05:15.450 --> 05:20.700 us them the opposite of mask three or so all elements but not Element Six and Seven 05:23.750 --> 05:26.400 back and sit here so six and seven are missing. 05:27.180 --> 05:27.540 All right. 05:27.540 --> 05:33.300 So this is set for boolean indexing and in the next session we will learn about how to create random 05:33.300 --> 05:35.040 numbers with NUM pi. 05:35.040 --> 05:35.640 See you there.