# R List: How to Create a List in R Programming & Select Elements

## What is R List?

R List is an object in R programming which includes matrices, vectors, data frames, or lists within it. R List is also used to store a collection of objects and use them when we need them. We can imagine the R list as a bag to put many different items. When we need to use an item, we can open the bag and use it.

### Syntax of List in R

We can use list() function to create lists in R programming:

```list(element_1, ...)
arguments:
-element_1: store any type of R object
-...: pass as many objects as specifying. each object needs to be separated by a comma```

In this R List tutorial, we will learn:

## How to Create a List in R

Below is a step by step process on how to create a list in R:

In the example below, we will create three different objects, a Vector, a Matrix and a Data Frame using list function in R.

Step 1) Create a Vector

Use the below code to create a vector in R

```# Vector with numeric from 1 up to 5
vect  <- 1:5```

Step 2) Create a Matrix

Now, create a matrix using the folloing code

```# A 2x 5 matrix
mat  <- matrix(1:9, ncol = 5)
dim(mat)```

Output:

`##  2 5`

Step 3) Create Data Frame

Create a data frame in R using below code

```# select the 10th row of the built-in R data set EuStockMarkets
df <- EuStockMarkets[1:10,]```

Step 4) Create a List in R

Now, we can put the three object into R list using below code

```# Construct list with these vec, mat, and df:
my_list <- list(vect, mat, df)
my_list```

Output:

```## []
##  1 2 3 4 5

## []
##       [,1] [,2] [,3] [,4] [,5]
## [1,]    1    3    5    7    9
## [2,]    2    4    6    8    1

## []
##          DAX    SMI    CAC   FTSE
##  [1,] 1628.75 1678.1 1772.8 2443.6
##  [2,] 1613.63 1688.5 1750.5 2460.2
##  [3,] 1606.51 1678.6 1718.0 2448.2
##  [4,] 1621.04 1684.1 1708.1 2470.4
##  [5,] 1618.16 1686.6 1723.1 2484.7
##  [6,] 1610.61 1671.6 1714.3 2466.8
##  [7,] 1630.75 1682.9 1734.5 2487.9
##  [8,] 1640.17 1703.6 1757.4 2508.4
##  [9,] 1635.47 1697.5 1754.0 2510.5
##  [10,] 1645.89 1716.3 1754.3 2497.4

```

## Select Elements from R List

After we built our list, we can access it quite easily. We need to use the [[index]] to select an element in a list. The value inside the double square bracket represents the position of the item in a list we want to extract. For instance, we pass 2 inside the parenthesis, R returns the second element listed.

Now in this R tutorial, let’s try to select the second items of lists in R named my_list, we use my_list[]

```# Print second element of the list
my_list[]```

Output:

```##      [,1] [,2] [,3] [,4] [,5]
## [1,]    1    3    5    7    9
## [2,]    2    4    6    8    1
```

## Built-in Data Frame in R

Before creating our own data frame, we can have a look at the R data set available online. The prison dataset is a 714×5 dimension. We can get a quick look at the bottom of the data frame with tail() function. By analogy, head() displays the top of the data frame. You can specify the number of rows shown with head (df, 5). We will learn more about the function read.csv() in future tutorial.

```PATH <-'https://raw.githubusercontent.com/guru99-edu/R-Programming/master/prison.csv'
```

Output:

```##   X state year govelec black
## 1 1     1   80       0 0.2560
## 2 2     1   81       0 0.2557
## 3 3     1   82       1 0.2554
## 4 4     1   83       0 0.2551
## 5 5     1   84       0 0.2548

```

We can check the structure of the data frame with str:

```# Structure of the data
str(df)```

Output:

```## 'data.frame':    714 obs. of  5 variables:
##  \$ X      : int  1 2 3 4 5 6 7 8 9 10 ...
##  \$ state  : int  1 1 1 1 1 1 1 1 1 1 ...
##  \$ year   : int  80 81 82 83 84 85 86 87 88 89 ...
##  \$ govelec: int  0 0 1 0 0 0 1 0 0 0 ...
##  \$ black  : num  0.256 0.256 0.255 0.255 0.255 ...

```

All variables are stored in the numerical format.

## Summary

• R List is an object in R programming which includes matrices, vectors, data frames, or lists within it.
• The list() function is used to create lists in R programming.
• We can use the [[index]] function to select an element in a list. The value inside the double square bracket represents the position of the item in a list we want to extract.
• We can get a quick look at the bottom of the data frame with tail() function.