1
00:00:04,500 --> 00:00:07,750
So far, all of our output
values and variables

2
00:00:07,750 --> 00:00:09,990
have been single numbers.

3
00:00:09,990 --> 00:00:13,790
You can also create more
advanced data structures in R

4
00:00:13,790 --> 00:00:16,860
like vectors and data frames.

5
00:00:16,860 --> 00:00:20,790
A vector is a series of
numbers or characters

6
00:00:20,790 --> 00:00:23,390
stored as the same object.

7
00:00:23,390 --> 00:00:27,540
You can create a vector in R
using the c function, which

8
00:00:27,540 --> 00:00:29,990
stands for combine.

9
00:00:29,990 --> 00:00:46,090
In your R console, type
c(2,3,5,8,13) and hit Enter.

10
00:00:46,090 --> 00:00:49,960
This creates a vector of
five numbers all stored

11
00:00:49,960 --> 00:00:52,610
as the same object.

12
00:00:52,610 --> 00:00:55,040
To learn more
about vectors in R,

13
00:00:55,040 --> 00:00:59,000
let's enter some data into R
about the life expectancies

14
00:00:59,000 --> 00:01:01,010
in different countries.

15
00:01:01,010 --> 00:01:04,420
We'll first create a vector
of country names called

16
00:01:04,420 --> 00:01:07,740
Country using the c function.

17
00:01:07,740 --> 00:01:10,720
We'll put each
country name in quotes

18
00:01:10,720 --> 00:01:14,680
since we are typing
characters not numbers.

19
00:01:14,680 --> 00:01:19,970
So in your R
console, type Country

20
00:01:19,970 --> 00:01:26,240
equals and then c for the
combine function, parentheses

21
00:01:26,240 --> 00:01:44,880
and then "Brazil", "China",
"India", "Switzerland",

22
00:01:44,880 --> 00:01:47,560
and then "USA".

23
00:01:47,560 --> 00:01:51,009
Close the parentheses
and hit Enter.

24
00:01:51,009 --> 00:01:53,890
Now, let's create
a second vector.

25
00:01:53,890 --> 00:01:55,890
This time with the
life expectancies

26
00:01:55,890 --> 00:01:59,390
of these five countries
in the same order

27
00:01:59,390 --> 00:02:01,800
that we entered
the country names.

28
00:02:01,800 --> 00:02:08,610
We'll call this one
LifeExpectancy =

29
00:02:08,610 --> 00:02:26,040
c(74,76,65,83,79) and hit Enter.

30
00:02:26,040 --> 00:02:33,160
Now if you take a look at both
Country and LifeExpectancy,

31
00:02:33,160 --> 00:02:36,960
you can see that Country
has five character values

32
00:02:36,960 --> 00:02:41,970
and LifeExpectancy has
five numerical values.

33
00:02:41,970 --> 00:02:44,020
A word of warning--
you shouldn't

34
00:02:44,020 --> 00:02:48,420
try to combine characters and
numbers in the same vector.

35
00:02:48,420 --> 00:02:52,060
R only allows one data
type in each vector

36
00:02:52,060 --> 00:02:55,670
so all of the numbers will
be converted to characters.

37
00:02:55,670 --> 00:02:57,520
This is bad because
it won't allow

38
00:02:57,520 --> 00:03:01,120
us to do any numerical
calculations with the numbers,

39
00:03:01,120 --> 00:03:03,780
like compute the mean.

40
00:03:03,780 --> 00:03:06,750
If you want to display
an element of a vector,

41
00:03:06,750 --> 00:03:08,380
use square brackets.

42
00:03:08,380 --> 00:03:15,160
For example, we could type
CountryCountry[1] to get the first

43
00:03:15,160 --> 00:03:18,480
element of the Country
vector, Brazil.

44
00:03:18,480 --> 00:03:25,160
Or we could type
LifeExpectancyLifeExpectancy[3] to get

45
00:03:25,160 --> 00:03:29,180
the third element of
LifeExpectancy, 65,

46
00:03:29,180 --> 00:03:32,800
corresponding to India.

47
00:03:32,800 --> 00:03:36,100
Another nice function
to create vectors in R

48
00:03:36,100 --> 00:03:41,110
is the seq function which
creates a sequence of numbers.

49
00:03:41,110 --> 00:03:50,290
Try typing seq(0,100,2).

50
00:03:50,290 --> 00:03:53,520
Close the parentheses
and hit Enter.

51
00:03:53,520 --> 00:03:57,980
This gives a sequence of
numbers from 0 to 100,

52
00:03:57,980 --> 00:04:02,510
starting at zero, the first
argument to the seq function,

53
00:04:02,510 --> 00:04:07,340
ending at 100, the second
argument to the seq function,

54
00:04:07,340 --> 00:04:10,080
and the numbers are
in increments of two,

55
00:04:10,080 --> 00:04:13,340
the third argument
to the seq function.

56
00:04:13,340 --> 00:04:15,750
This can be useful
if you want to create

57
00:04:15,750 --> 00:04:20,200
a unique identifier
for observations.

58
00:04:20,200 --> 00:04:22,950
Now, let's combine
our vectors into what

59
00:04:22,950 --> 00:04:27,550
we call a data frame in R.
This will be an important data

60
00:04:27,550 --> 00:04:29,940
structure for us
because all of the data

61
00:04:29,940 --> 00:04:32,280
files we'll work
with in this course

62
00:04:32,280 --> 00:04:34,810
will be loaded as data frames.

63
00:04:34,810 --> 00:04:39,500
Additionally, many algorithms
in R require all of the data

64
00:04:39,500 --> 00:04:43,540
to be in a single object
like a data frame.

65
00:04:43,540 --> 00:04:48,280
We'll call our data
frame CountryData

66
00:04:48,280 --> 00:04:52,580
and then use the
data.frame function

67
00:04:52,580 --> 00:04:56,909
to combine Country
and LifeExpectancy.

68
00:04:56,909 --> 00:05:01,710
So after typing
CountryData = data.frame,

69
00:05:01,710 --> 00:05:06,520
in parentheses type Country
comma LifeExpectancy.

70
00:05:09,800 --> 00:05:12,760
Then close the
parentheses and hit Enter.

71
00:05:12,760 --> 00:05:16,740
Let's take a look at CountryData
by typing CountryData

72
00:05:16,740 --> 00:05:18,470
and hitting Enter.

73
00:05:18,470 --> 00:05:21,370
It has two columns,
our variables,

74
00:05:21,370 --> 00:05:24,630
and five rows, our observations.

75
00:05:24,630 --> 00:05:27,070
It's similar to how
you might organize data

76
00:05:27,070 --> 00:05:31,140
in a spreadsheet
software like Excel.

77
00:05:31,140 --> 00:05:34,380
Let's say we now want to add
another variable to our data

78
00:05:34,380 --> 00:05:39,110
frame-- the population in
thousands of each country.

79
00:05:39,110 --> 00:05:41,659
We can do this by
using a dollar sign

80
00:05:41,659 --> 00:05:44,870
to link the new data
into the data frame.

81
00:05:44,870 --> 00:05:49,409
So we'll type the name of
our data frame, CountryData,

82
00:05:49,409 --> 00:05:52,260
and then a dollar sign
followed by the name

83
00:05:52,260 --> 00:05:55,590
of the new variable we
want to add, Population.

84
00:05:58,390 --> 00:06:02,700
Then we'll set this equal
to c, and in parentheses

85
00:06:02,700 --> 00:06:06,210
the population in
thousands of each country.

86
00:06:06,210 --> 00:06:29,650
So 199000, 1390000,
1240000, 7997, and 318000.

87
00:06:29,650 --> 00:06:32,640
Close the parentheses
and hit Enter.

88
00:06:32,640 --> 00:06:36,210
Now if you take a
look at CountryData

89
00:06:36,210 --> 00:06:40,690
you should see that we have
a third column, Population.

90
00:06:40,690 --> 00:06:43,590
We'll use this dollar
sign notation a lot

91
00:06:43,590 --> 00:06:46,860
and we'll talk about it
more later in this lecture.

92
00:06:46,860 --> 00:06:49,320
Note that we had to give
the population values

93
00:06:49,320 --> 00:06:51,090
in the correct order.

94
00:06:51,090 --> 00:06:56,030
R will just combine the vectors
in the order they're typed.

95
00:06:56,030 --> 00:07:00,760
Now, suppose we want to add two
new observations for Australia

96
00:07:00,760 --> 00:07:02,290
and Greece.

97
00:07:02,290 --> 00:07:06,240
We first need to create
new Country, LifeExpectancy

98
00:07:06,240 --> 00:07:08,470
and Population vectors.

99
00:07:08,470 --> 00:07:11,850
So we will now set
Country equal to the names

100
00:07:11,850 --> 00:07:21,050
of the new countries,
Australia and Greece.

101
00:07:25,790 --> 00:07:31,770
We'll set LifeExpectancy equal
to the new life expectancies,

102
00:07:31,770 --> 00:07:39,640
82 and 81, and we'll
call Population

103
00:07:39,640 --> 00:07:44,950
a vector of the populations
of these countries 23050

104
00:07:44,950 --> 00:07:48,840
and 11125.

105
00:07:48,840 --> 00:07:51,770
Then we can create
a new data frame.

106
00:07:51,770 --> 00:07:56,110
We'll call this one
NewCountryData and we'll set it

107
00:07:56,110 --> 00:07:58,490
equal to data.frame(Country,
LifeExpectancy, Population).

108
00:08:15,170 --> 00:08:17,530
Note that we combined
three vectors here

109
00:08:17,530 --> 00:08:20,100
with the data.frame function.

110
00:08:20,100 --> 00:08:25,770
If we take a look
at NewCountryData,

111
00:08:25,770 --> 00:08:30,320
we can see that it's very
similar to CountryData.

112
00:08:30,320 --> 00:08:34,570
Lastly, let's combine
CountryData and NewCountryData

113
00:08:34,570 --> 00:08:37,750
with the rbind
function which combines

114
00:08:37,750 --> 00:08:40,700
data frames by
stacking the rows.

115
00:08:40,700 --> 00:08:46,580
We'll call this new data
frame AllCountryData

116
00:08:46,580 --> 00:08:50,720
and we'll use the rbind
function to combine

117
00:08:50,720 --> 00:08:54,050
CountryData, and NewCountryData.

118
00:09:00,320 --> 00:09:05,360
If we take a look
at AllCountryData

119
00:09:05,360 --> 00:09:09,570
we can see that it has the
three variables from before

120
00:09:09,570 --> 00:09:12,950
and all seven observations.

121
00:09:12,950 --> 00:09:15,220
The functions we've
used in this video

122
00:09:15,220 --> 00:09:17,640
have allowed us to
create data structures

123
00:09:17,640 --> 00:09:21,950
and modify data structures
in R. But most of the time

124
00:09:21,950 --> 00:09:24,970
you'll be reading in data
from an external file, which

125
00:09:24,970 --> 00:09:27,550
we'll do in the next video.