--Basics

The basic data structures in R can be organized by their dimensionality (1D, 2D, …, nD)

#Identifying the Data Structure

# different data structures
vector <- 1:10
list <- list(item1 = 1:10, item2 = LETTERS[1:18])
matrix <- matrix(1:12, nrow = 4)   
df <- data.frame(item1 = 1:18, item2 = LETTERS[1:18])

# identify the structure of each object
str(vector)
##  int [1:10] 1 2 3 4 5 6 7 8 9 10

str(list)
## List of 2
##  $ item1: int [1:10] 1 2 3 4 5 6 7 8 9 10
##  $ item2: chr [1:18] "A" "B" "C" "D" ...

str(matrix)
##  int [1:4, 1:3] 1 2 3 4 5 6 7 8 9 10 ...

str(df)
## 'data.frame':	18 obs. of  2 variables:
##  $ item1: int  1 2 3 4 5 6 7 8 9 10 ...
##  $ item2: Factor w/ 18 levels "A","B","C","D",..: 
## 1 2 3 4 5 6 7 8 9 10 ...

You can also use class

#Understanding Attributes

Some examples of R object attributes are:

• names, dimnames

• dimensions (e.g. matrices, arrays)

• class (e.g. integer, numeric)

• length

• other user-defined attributes/metadata

Attributes of an object (if any) can be accessed using the attributes()function. Not all R objects contain attributes, in which case the attributes()function returns NULL.

# assess attributes of an object
attributes(df)
## $names
## [1] "item1" "item2"
## 
## $row.names
##  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
## 
## $class
## [1] "data.frame"

attributes(matrix)
## $dim
## [1] 4 3

# assess names of an object
names(df)
## [1] "item1" "item2"

# assess the dimensions of an object
dim(matrix)
## [1] 4 3

# assess the class of an object
class(list)
## [1] "list"

# access the length of an object
length(vector)
## [1] 10

# note that length will measure the number of items in
# a list or number of columns in a data frame
length(list)
## [1] 2

length(df)
## [1] 2

#Exercises:

1. Identify the data structure and attributes for the built-in sleep data set.

2. Identify the data structure and attributes for the built-in state.name data set.

3. Identify the data structure and attributes for the built-in Harman74.cordata set.

4. Identify the data structure and attributes for the built-in WorldPhones data set.

5. Bonus: Identify the data structure and attributes for the built-in Nile data set. What kind of data object is this?