Page 44 - Applied Statistics with R

44 CHAPTER 3. DATA AND PROGRAMMING

example_data

## x y z
## 1 1 Hello TRUE
## 2 3 Hello FALSE
## 3 5 Hello TRUE
## 4 7 Hello FALSE
## 5 9 Hello TRUE
## 6 1 Hello FALSE
## 7 3 Hello TRUE
## 8 5 Hello FALSE
## 9 7 Hello TRUE
## 10 9 Goodbye FALSE

Unlike a list which has more flexibility, the elements of a data frame must all
be vectors, and have the same length.
example_data$x

## [1] 1 3 5 7 9 1 3 5 7 9

all.equal(length(example_data$x),
length(example_data$y),
length(example_data$z))

## [1] TRUE

str(example_data)

## 'data.frame': 10 obs. of 3 variables:
## $ x: num 1 3 5 7 9 1 3 5 7 9
## $ y: chr "Hello" "Hello" "Hello" "Hello" ...
## $ z: logi TRUE FALSE TRUE FALSE TRUE FALSE ...
nrow(example_data)

## [1] 10

ncol(example_data)

## [1] 3