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
What is R List? How to Create a List in R Select Elements from R List Built-in Data Frame in R
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. 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:
[1] 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]]
[1] 1 2 3 4 5
[[2]]
[,1] [,2] [,3] [,4] [,5]
[1,] 1 3 5 7 9
[2,] 2 4 6 8 1
[[3]]
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
Now in this R tutorial, let’s try to select the second items of lists in R named my_list, we use my_list[[2]]
Print second element of the list
my_list[[2]]
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' df <- read.csv(PATH)[1:5] head(df, 5)
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.
