Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,570 --> 00:00:06,560 Hello everyone and welcome to the lecture on vector indexing and slicing and this lecture on learn how 2 00:00:06,550 --> 00:00:11,960 to use bracket notation to index and access individual elements from a vector. 3 00:00:11,970 --> 00:00:14,520 Let's go ahead and jump to our studio. 4 00:00:14,520 --> 00:00:14,840 All right. 5 00:00:14,850 --> 00:00:17,660 So here we are our studio and to start things off. 6 00:00:17,700 --> 00:00:24,090 I'm just going to go ahead and make vectors the one and the two will say V-1. 7 00:00:24,120 --> 00:00:34,080 It's just a numeric vector consisting of 100 200 and 300 and we'll say vector V-2 is a vector with a 8 00:00:34,080 --> 00:00:36,600 b and c is a character vector. 9 00:00:37,440 --> 00:00:40,590 So A B C. 10 00:00:40,700 --> 00:00:41,360 All right. 11 00:00:41,550 --> 00:00:48,240 So we have the one we have the to know what we're going to do is learn how to use bracket notation to 12 00:00:48,300 --> 00:00:48,930 index. 13 00:00:48,930 --> 00:00:55,330 So indexing works by using brackets and then passing the index position of the element as a number. 14 00:00:55,480 --> 00:01:01,430 And keep in mind that indexing and are starts at 1 and some other programming languages such as Python 15 00:01:01,440 --> 00:01:03,170 indexing starts at zero. 16 00:01:03,270 --> 00:01:05,070 That in our IT STARTS AT 1. 17 00:01:05,070 --> 00:01:08,760 So let me go ahead and show you an example of how to grab elements from a vector. 18 00:01:09,090 --> 00:01:14,640 You'll put in the vector and then you'll use square brackets and then you'll pass in the index of the 19 00:01:14,640 --> 00:01:15,810 element you want. 20 00:01:16,020 --> 00:01:21,280 So for example let's say you want the elements 200 in the vector of the one. 21 00:01:21,480 --> 00:01:24,770 So it's at position to this in the second position. 22 00:01:24,840 --> 00:01:31,020 So I input the index two inside of my square brackets and it returns to me the elements at that index 23 00:01:31,020 --> 00:01:31,710 . 24 00:01:31,710 --> 00:01:35,140 So let's do another example let's say I wanted the letter C. 25 00:01:35,340 --> 00:01:41,640 So that's an vector v 2 and in square brackets I'm going to input 3 because it's at the third position 26 00:01:41,650 --> 00:01:42,250 . 27 00:01:42,950 --> 00:01:43,420 OK. 28 00:01:43,500 --> 00:01:49,070 And then it returns that particular elements as far as slicing. 29 00:01:49,080 --> 00:01:53,940 That means we're going to do basically multiple indexing so we can grab multiple items from a vector 30 00:01:54,240 --> 00:01:58,500 by actually passing a vector of index positions inside the square brackets. 31 00:01:58,500 --> 00:02:04,380 Let's go ahead and show an example of that first thing to do is just clear the consul showed the one 32 00:02:05,460 --> 00:02:07,130 and showed it to. 33 00:02:07,350 --> 00:02:07,870 All right. 34 00:02:08,010 --> 00:02:12,350 So let's go ahead and grab the numbers 100 and 200. 35 00:02:12,420 --> 00:02:14,430 So those are from Vector 1. 36 00:02:14,720 --> 00:02:19,860 And if I just put in a single number I'll return a single element but to grab an actual slice of that 37 00:02:19,860 --> 00:02:26,490 vector I can pass in a vector inside of the square brackets and this vector will just be a vector of 38 00:02:27,150 --> 00:02:28,140 index positions. 39 00:02:28,140 --> 00:02:33,030 So I want to grab the first element and the second element and that's what occurs. 40 00:02:33,030 --> 00:02:36,750 So let's say I wanted to grab the letters A and see. 41 00:02:37,050 --> 00:02:39,040 So that's in Dr. V-2. 42 00:02:39,270 --> 00:02:45,010 I put in my square brackets to notate that I'm using indexing and then I want to grab and see. 43 00:02:45,020 --> 00:02:48,080 So that's the first element and the third elements. 44 00:02:48,270 --> 00:02:50,010 So I'm going to go ahead and put in a vector. 45 00:02:50,010 --> 00:02:56,100 Notice I'm using the combined function to specify that it's a vector and I'm going to go ahead and grab 46 00:02:56,670 --> 00:02:58,360 a and c in that manner. 47 00:02:58,590 --> 00:03:02,770 So that's how you can grab multiple items from a vector. 48 00:03:03,120 --> 00:03:09,690 So you heard me use the term slicing earlier and what I mean by slicing is not just any multiple indexing 49 00:03:09,720 --> 00:03:13,860 It's when you can actually grab a continuous slice of vector. 50 00:03:13,860 --> 00:03:16,850 So let's go ahead and show you how you can do that in order to do that. 51 00:03:16,860 --> 00:03:19,480 I'm going to go ahead and create a longer vector. 52 00:03:19,680 --> 00:03:21,960 We'll call this just the. 53 00:03:22,650 --> 00:03:25,830 And we'll do it on the numbers one through ten. 54 00:03:25,830 --> 00:03:28,640 One two three four five six seven eight nine. 55 00:03:28,750 --> 00:03:33,600 And then finally 10 there are actually easier easier and better ways to create such a vector which will 56 00:03:33,600 --> 00:03:35,140 show you later on in the course. 57 00:03:35,160 --> 00:03:38,420 But for now we'll just use than normal combine function. 58 00:03:38,460 --> 00:03:41,280 So my vector which is the numbers 1 through 10. 59 00:03:41,430 --> 00:03:46,980 And let's actually want to grab a slice so that continuous slice of elements I can use that using a 60 00:03:46,980 --> 00:03:48,170 colon notation. 61 00:03:48,180 --> 00:03:54,600 So I'm going to use square brackets again and then the weight of notation or syntax works as you put 62 00:03:54,600 --> 00:03:55,830 your starting index. 63 00:03:55,830 --> 00:03:58,830 So let's say I want to grab the numbers 2 3 and 4. 64 00:03:58,890 --> 00:04:04,380 So I want to start a position to then I'm going to put in the colon and then put my stopping index. 65 00:04:04,380 --> 00:04:06,100 So I want to stop at four. 66 00:04:06,600 --> 00:04:09,640 So this will return the numbers 2 3 and 4. 67 00:04:10,170 --> 00:04:11,990 So that's going to grab that slice. 68 00:04:12,000 --> 00:04:13,590 Let's go ahead and show another example. 69 00:04:13,620 --> 00:04:17,810 Let's say I wanted to grab the elements 7 8 9 and 10. 70 00:04:17,880 --> 00:04:25,710 So output outputted my vector put in square brackets and I want to start at index position 7 and ends 71 00:04:26,040 --> 00:04:28,240 or stop in the x position 10. 72 00:04:28,470 --> 00:04:34,090 So that's going to be my slice and I get in return 7 8 9 and 10. 73 00:04:34,260 --> 00:04:41,340 Now previously in the course we discussed using names to name the elements in our vector such as that 74 00:04:41,340 --> 00:04:43,340 temperature vector we saw earlier. 75 00:04:43,500 --> 00:04:46,980 We can actually use those names as index marks. 76 00:04:46,980 --> 00:04:52,180 So let's go ahead and show how you can index elements using names in order to do this. 77 00:04:52,230 --> 00:04:58,880 I'm going to go ahead and reassign V as just a simple vector of numerics we'll call it one two three 78 00:04:58,910 --> 00:05:05,240 four and then I'm going to use the names function on the. 79 00:05:05,670 --> 00:05:09,380 And I'm going to go ahead and pass on a vector of just names. 80 00:05:09,380 --> 00:05:13,690 In this case it'll just be simple letters to designate the names for each of those elements. 81 00:05:13,920 --> 00:05:20,070 So say B C D and make sure to put some quotes around that. 82 00:05:20,160 --> 00:05:20,700 And there we go. 83 00:05:20,700 --> 00:05:25,800 So now if I look at V it has those named elements 1 2 3 4. 84 00:05:25,830 --> 00:05:35,520 So instead of having to do something like the two which will return that names element B to what I can 85 00:05:35,520 --> 00:05:44,030 do is actually pass in the name of the elements I want so element 2 is going to be named B. 86 00:05:44,040 --> 00:05:50,310 So instead of passing in an index it can actually pass in the name B and I'll get that also back in 87 00:05:50,310 --> 00:05:52,120 return the same way. 88 00:05:52,290 --> 00:05:55,860 And if you want to do multiple indexing you can actually pass in a vector. 89 00:05:56,100 --> 00:06:01,990 So I can do something like this I can save the square brackets combine function and then pass in of 90 00:06:02,010 --> 00:06:03,790 vectors of names. 91 00:06:04,020 --> 00:06:05,930 So I can do this actually out of order. 92 00:06:05,940 --> 00:06:15,480 Let's go ahead and say I want names see the element name Z and the element names a and r is going to 93 00:06:15,480 --> 00:06:21,090 return those named elements in the same order as I requested them in that vector. 94 00:06:21,100 --> 00:06:26,320 OK so now let's do a brief discussion on comparison operators and selection. 95 00:06:26,610 --> 00:06:32,100 So as we discussed in the comparison operator lecture we can use comparison operators to filter out 96 00:06:32,160 --> 00:06:33,930 elements from a vector. 97 00:06:33,930 --> 00:06:38,910 Sometimes this is also referred to as boolean or logical masking because you're essentially creating 98 00:06:38,910 --> 00:06:42,130 a vector of logicals to filter out results you want. 99 00:06:42,330 --> 00:06:44,320 Let's go ahead and see an example. 100 00:06:44,560 --> 00:06:50,520 We'll use the same vector we've been working with the ABC 1 2 3 4. 101 00:06:50,580 --> 00:06:56,540 So let's say I wanted to filter out any values that were less than 2. 102 00:06:56,670 --> 00:07:01,460 So I wanted to only grab values that were greater than two in this case going to be three and four. 103 00:07:01,650 --> 00:07:04,580 I can do that same bracket notation. 104 00:07:04,620 --> 00:07:09,990 In this case I just do a comparison operator inside of that bracket notation. 105 00:07:09,990 --> 00:07:12,380 So it kind of looks like this. 106 00:07:12,450 --> 00:07:17,730 Now I have the square brackets and then a comparison condition here. 107 00:07:17,790 --> 00:07:21,660 So basically says Return V were V is greater than 2. 108 00:07:22,020 --> 00:07:28,490 So if I click enter I see that C and D name which are both greater than two three and four then returns 109 00:07:28,550 --> 00:07:29,190 . 110 00:07:29,220 --> 00:07:34,290 So to break down and see how this actually works let's first show what is returned if we just say V 111 00:07:34,290 --> 00:07:36,730 is greater than 2. 112 00:07:36,780 --> 00:07:38,730 So if I say V is greater than 2. 113 00:07:38,760 --> 00:07:42,980 Notice I get a logical vector out I get false false. 114 00:07:42,990 --> 00:07:45,100 True true. 115 00:07:45,190 --> 00:07:49,680 And so what this means is that we're basically passing this vector of logicals through the brackets 116 00:07:49,680 --> 00:07:54,630 of the vector and only return TRUE values at the matching index positions. 117 00:07:54,630 --> 00:08:00,750 What's also nice about this is we can assign that condition that logical comparison to a variable name 118 00:08:01,050 --> 00:08:03,750 and then just pass in that variable name and the brackets. 119 00:08:03,750 --> 00:08:07,080 So for example I could say something like this. 120 00:08:07,320 --> 00:08:16,580 I could say filter Let's actually call this something assholes call it my filter. 121 00:08:16,880 --> 00:08:24,420 So you don't overwrite any builtin functionality will say my filter will go ahead and put in the logical 122 00:08:24,420 --> 00:08:28,440 comparison I will say the is greater than 2. 123 00:08:29,490 --> 00:08:30,860 So now it's my filter. 124 00:08:30,870 --> 00:08:34,650 And if you notice then my filter is just this vector. 125 00:08:34,650 --> 00:08:46,020 So I can then say when it clear that the pass in my filter and it'll return where those explanations 126 00:08:46,140 --> 00:08:46,920 are true. 127 00:08:46,920 --> 00:08:48,890 So in this case it's C and D. 128 00:08:49,170 --> 00:08:53,970 So this is really nice because you can start to name your comparison operators are these logical conditioned 129 00:08:53,970 --> 00:08:56,880 statements pass them into vectors that have names. 130 00:08:56,910 --> 00:09:00,530 So everything becomes a lot more readable later on in your code. 131 00:09:00,540 --> 00:09:01,160 All right. 132 00:09:01,380 --> 00:09:03,360 So that's it for this lecture. 133 00:09:03,360 --> 00:09:05,620 Just a brief overview of what we've covered. 134 00:09:05,790 --> 00:09:10,870 We learned how we can use bracket notation to index and access individual elements from a vector. 135 00:09:10,960 --> 00:09:15,810 We learned how we can use that same notation for multiple indexing by passing a vector inside of those 136 00:09:15,810 --> 00:09:16,860 brackets. 137 00:09:16,860 --> 00:09:22,620 And we also learn how to use slicing with that colon in order to grab a continuous slice of the vector 138 00:09:23,100 --> 00:09:28,890 and then finally we learn how we can index of names and also use comparison operators in logical conditions 139 00:09:28,890 --> 00:09:32,850 statements to filter out results from a vector. 140 00:09:32,850 --> 00:09:35,760 All right thanks everyone and I'll see you at the next lecture 14390