Chapter 20

Introduction

Vector basics

Important type of atomic vectors

Using atomic vectors

sample(10)+10
##  [1] 19 15 11 12 14 17 13 18 16 20
1:10 + 1:2
##  [1]  2  4  4  6  6  8  8 10 10 12
1:10 + 1:3
## Warning in 1:10 + 1:3: longer object length is not a multiple of shorter object
## length
##  [1]  2  4  6  5  7  9  8 10 12 11
data.frame(a = 1:10, b = 1:2)
##     a b
## 1   1 1
## 2   2 2
## 3   3 1
## 4   4 2
## 5   5 1
## 6   6 2
## 7   7 1
## 8   8 2
## 9   9 1
## 10 10 2
#data.frame(a = 1:10, b = 1:3)
x <- sample(10)
x
##  [1]  1  9  3  2  7  4  6  8  5 10
x[c(5, 7)]
## [1] 7 6
x[x>5]
## [1]  9  7  6  8 10

recursive vectors

a <- list(a = 1:3, b = "a string", c = pi, d = list(-1, -5))
a
## $a
## [1] 1 2 3
## 
## $b
## [1] "a string"
## 
## $c
## [1] 3.141593
## 
## $d
## $d[[1]]
## [1] -1
## 
## $d[[2]]
## [1] -5
a[1:2]
## $a
## [1] 1 2 3
## 
## $b
## [1] "a string"
a[[4]]
## [[1]]
## [1] -1
## 
## [[2]]
## [1] -5
a[[4]][2]
## [[1]]
## [1] -5
a[[4]][[2]]
## [1] -5

Attributes

Augmented Vectors

Chapter 21 iteration

Introduction

four loop

# Example from cheat sheet
for (i in 1:4) {
    j <- i+10
    print(j)
}
## [1] 11
## [1] 12
## [1] 13
## [1] 14
#example 1: numeric calculation - add 10
x<- 11:15

for (i in seq_along(x)) {
    j <- x [i] +10
    print(j)
    
}
## [1] 21
## [1] 22
## [1] 23
## [1] 24
## [1] 25
#save output
y <- vector("integer", length(x))

for (i in seq_along(x)) {
    y <- x[i] +10
    print(y)
}
## [1] 21
## [1] 22
## [1] 23
## [1] 24
## [1] 25
# output
y
## [1] 25
#example 2: string operation- extract first letter
x <- c("abc", "xyz")

y <- vector("character", length(x))

for (i in seq_along(x)) {
    y <- x[i] %>% str_extract("[a-z]")
    print(y[i])
}
## [1] "a"
## [1] NA
# Output 
y
## [1] "x"

The map Functions

#example 1: numeric calculation - add 10
x<- 11:15 

y <- vector("integer", length(x))

for (i in seq_along(x)) {
    y <- x[i] +10
    print(y)
}
## [1] 21
## [1] 22
## [1] 23
## [1] 24
## [1] 25
# output 
y
## [1] 25
# using map functions
x
## [1] 11 12 13 14 15
map(.x = x, .f= ~ .x + 10)
## [[1]]
## [1] 21
## 
## [[2]]
## [1] 22
## 
## [[3]]
## [1] 23
## 
## [[4]]
## [1] 24
## 
## [[5]]
## [1] 25
map_dbl(.x = x, .f= ~ .x + 10)
## [1] 21 22 23 24 25
add_10 <- function(x) {x+10}
11 %>% add_10()
## [1] 21
map_dbl(.x = x, .f = add_10)
## [1] 21 22 23 24 25