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# --Basics

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

![](/files/-LLoPWky14XZ8p-jqpkl)

## #Identifying the Data Structure

```r
# 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 ...
```

{% hint style="info" %}
&#x20;You can also use `class`
{% endhint %}

## #Understanding Attributes

&#x20;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

{% hint style="info" %}
&#x20;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.
{% endhint %}

```r
# 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.cor`data 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?