1. Vector
One-Dimensional Array
c(1, 1.3, 8)
## [1] 1.0 1.3 8.0
x = 2:5
x
## [1] 2 3 4 5
x^2 + 1/4
## [1] 4.25 9.25 16.25 25.25
Class function helps us understand the type of object
class(x)
## [1] "integer"
The set.seed() function gurantees that the same random values are
produced each time.
set.seed(2021)
y = sample(1:50)
y
## [1] 7 38 46 39 12 6 49 44 5 47 23 48 18 3 26 22 31 19 4 21 35 42 9 45 43
## [26] 11 36 27 30 40 15 2 24 16 20 1 8 17 34 29 32 10 41 37 50 33 13 25 28 14
The summary() function reduces data frame to just one vector or
value.
summary(y)
## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 1.00 13.25 25.50 25.50 37.75 50.00
class(y)
## [1] "integer"
The str() function displays the contents of a list.
str(y)
## int [1:50] 7 38 46 39 12 6 49 44 5 47 ...
2. Data Frame
The head(x,y) function returns a table dataset which x is the data
and y is the amount of rows being displayed.
head(cars, 8)
## speed dist
## 1 4 2
## 2 4 10
## 3 7 4
## 4 7 22
## 5 8 16
## 6 9 10
## 7 10 18
## 8 10 26
class(cars)
## [1] "data.frame"
summary(cars)
## speed dist
## Min. : 4.0 Min. : 2.00
## 1st Qu.:12.0 1st Qu.: 26.00
## Median :15.0 Median : 36.00
## Mean :15.4 Mean : 42.98
## 3rd Qu.:19.0 3rd Qu.: 56.00
## Max. :25.0 Max. :120.00
summary(cars$speed)
## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 4.0 12.0 15.0 15.4 19.0 25.0
summary(cars$dist)
## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 2.00 26.00 36.00 42.98 56.00 120.00
The quantile(x,y) function divides a data set x in equal halves and
you can change the amount of halves with y.
quantile(speed)
## 0% 25% 50% 75% 100%
## 4 12 15 19 25
quantile(speed, probs=seq(0,1, by = 0.20))
## 0% 20% 40% 60% 80% 100%
## 4 11 14 17 20 25
sd(speed)
## [1] 5.287644
var(speed)
## [1] 27.95918
dist = cars$dist
##correlation
cor(speed, dist)
## [1] 0.8068949
str(cars)
## 'data.frame': 50 obs. of 2 variables:
## $ speed: num 4 4 7 7 8 9 10 10 10 11 ...
## $ dist : num 2 10 4 22 16 10 18 26 34 17 ...
The dim() function retrieves or sets the dimensions of an
object.
The View() function invokes a spreadsheet-style data viewer within
RStudio.
dim(cars)
## [1] 50 2
View(cars)
3. Data Subsets
The cars[1,] shows all columns but only in the first row
The cars[,1] shows all rows but only in the first column
The cars[,1:2] shows all rows but only columns 1 through 2.
cars[1,]
## speed dist
## 1 4 2
cars[,1]
## [1] 4 4 7 7 8 9 10 10 10 11 11 12 12 12 12 13 13 13 13 14 14 14 14 15 15
## [26] 15 16 16 17 17 17 18 18 18 18 19 19 19 20 20 20 20 20 22 23 24 24 24 24 25
cars[,1:2]
## speed dist
## 1 4 2
## 2 4 10
## 3 7 4
## 4 7 22
## 5 8 16
## 6 9 10
## 7 10 18
## 8 10 26
## 9 10 34
## 10 11 17
## 11 11 28
## 12 12 14
## 13 12 20
## 14 12 24
## 15 12 28
## 16 13 26
## 17 13 34
## 18 13 34
## 19 13 46
## 20 14 26
## 21 14 36
## 22 14 60
## 23 14 80
## 24 15 20
## 25 15 26
## 26 15 54
## 27 16 32
## 28 16 40
## 29 17 32
## 30 17 40
## 31 17 50
## 32 18 42
## 33 18 56
## 34 18 76
## 35 18 84
## 36 19 36
## 37 19 46
## 38 19 68
## 39 20 32
## 40 20 48
## 41 20 52
## 42 20 56
## 43 20 64
## 44 22 66
## 45 23 54
## 46 24 70
## 47 24 92
## 48 24 93
## 49 24 120
## 50 25 85
Distance is a subset of cars and its values 1-3 are shown below
cars$dist[1:3]
## [1] 2 10 4
The c() function is short for combine which then combines the values
2,8,4. The values in those corresponding rows are returned and in column
2.
cars[c(2,8,4), 2]
## [1] 10 26 22
The - infront of c() function acts a not or not include values
between 2-49.
cars[-c(2:49),]
## speed dist
## 1 4 2
## 50 25 85
The which() function returns the position of the value that
satisfies the given condition.
which.max(cars$speed)
## [1] 50
cars[which.max(cars$speed),"dist"]
## [1] 85
The %n% operator checks if the values of the first argument are
present in the second argument. Are the values included
in?
cars$dist %in% c(10,20)
## [1] FALSE TRUE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
## [13] TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE
## [25] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [37] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [49] FALSE FALSE
cars[cars$dist %in% c(10,20),]
## speed dist
## 2 4 10
## 6 9 10
## 13 12 20
## 24 15 20
4. Functions
f = function(x,y){
r = sqrt(x^2 + y^2)
return(10*sin(r)/r) # sin() returns the sine of a number in radians
}
f(3,4)
## [1] -1.917849
The Seq(from, to, by, length, along with) function generates a
sequence of numbers.
x = seq(-10, 10, length=30)
y=x
The outer(x,y,z) function is used to apply a function to two arrays.
x,y are the arrays. z is the function
z=outer(x,y,f)
The persp() function draws perspective plots of surfaces over the
x-y plane.
persp(x, y, z, theta = 30, phi = 30, expand = 0.5, col = "lightblue")
x=seq(-10,10,length=300)
The plot() function will plot two vectors against each other.
plot(x,sin(x))
