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Lists

Lists are the R objects with numbers, strings, vectors and another list or matrix inside it.

 

Creating  a List

Example to create a list containing numbers, strings, vectors and logical values.

#creating a list

list_info <- list(“Blue”, “Yellow”, c(12, 13, 14), TRUE, 13.12, 103.4)

print(list_info)

Output:

[[1]]

[1] “Blue”

 

[[2]]

[1] “Yellow”

 

[[3]]

[1] 12 13 14

 

[[4]]

[1] TRUE

 

[[5]]

[1] 13.12

 

[[6]]

[1] 103.4

Naming List Elements

Names can be given to list elements and can be accessed using the corresponding names.

Example:

#Creating  a list which contains a matrix and a vector

list_name <- list(matrix(c(1,2,3,4,5,6), nrow = 2), c(“mon”,”tue”,”wed”))

 

#Naming elements in the list

names(list_name) <- c(“Matrix”, “half_week”)

 

#displaying list

print(list_name)

Output:

$Matrix

     [,1] [,2] [,3]

[1,]    1    3   5

[2,]    2    4   6

 

$ half_week

[1] “mon” “tue” “wed”

Accessing List Elements

Index of the element of the list can be given access to Elements of the list.

Syntax:

list_name <- list(.,..,.)

names(list_name) <- c(.,.,.)

print(list_name[1])

Manipulating List Elements

Addition, subtraction or deleting and updating the list elements can be done;

Few examples are:

#Creating a list which contains a vector, a matrix and a list

list_name <- list(c(“Mon”, Tue”, “Wed”), matrix(c(2,1,1,1,5,6), nrow =2), list(“milk”, 1.2)

 

#Naming elements in the list

names(list_name) <- c(“half week”, “Matrix”, “A simple list”)

 

#Creating an element at the end of list

list_name [4] <- “An Element”

print(list_name[4])

 

#Withdrawing the last element

list_name[4] <-NULL

 

#Output last element

print(list_name[4])

Output:

[[1]]

[1] ” An Element

 

$

NULL

Merging Lists

Merging can be done by placing all lists into one list() function.

Example:

#Creating lists

lista <- list(2,4,6)

listb <- list(“Jan”, “Feb”, “Mar”)

 

#Merging lists

merge.list <- c(lista. listb)

 

#output merged list
print(merge.list)

Output:

[[1]]

[1] 2

 

[[2]]

[1] 4

 

[[3]]

[1] 6

 

[[4]]

[1] “Jan”

 

[[5]]

[1] “Feb”

 

[[6]]

[1] “Mar”

Converting List to Vector

Using unlist() function we can convert list to vector so that all the elements of the vector can be used for further manipulation such as applying arithmetic operations.

Example:

#Creating lists

lista <- list(1:3)

listb <- list(4:6)

 

#Converting lists to vector

cva <- unlist(lista)

cvb <- unlist(listb)

 

print(cva)

print(cvb)

Output:

[1] 1 2 3

[1] 4 5 6

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