Working with Lists in R

gist_list.R

# example 1: list containing vector and matrix
vect1 <- c('Jack', 'Jill', 'John')   # character vector
mat <- matrix(sample(12), nrow = 3)  # 3 x 4 matrix
list1 <- list(vect1, mat)            # list of 2 objects
list1

# example 2: coerce vector using as.list function
# numeric vector
vect1 <- 1:5                        

# coerce vect1 into list
list1 <- as.list(vect1)             
list1

# lists within list
# character vector
vect1 <- c('Jack', 'Jill', 'John')   

# 3 x 4 matrix
mat <- matrix(sample(12), nrow = 3)  

# list of 2 objects
list1 <- list(vect1, mat)           

# list that contains other lists
list2 <- list(vect1, mat, list1)
list2

# naming list elements
# character vector
vect1 <- c('Jack', 'Jill', 'John')          

# 3 x 4 matrix
mat <- matrix(sample(12), nrow = 3)          

# named list
list1 <- list(names = vect1, numbers = mat)  
list1

# describing lists
# character vector
vect1 <- c('Jack', 'Jill', 'John')                         

# 3 x 4 matrix
mat <- matrix(sample(12), nrow = 3)                        

# list of 2 objects
list1 <- list(vect1, mat) 
list1

# list containing other list
list2 <- list(names = vect1, numbers = mat, lists = list1)
list2


# class
class(list2)

# length of the list
length(list2)

# names of the elements in the list
names(list2)

# structure of the list
str(list2)


# index/subset list
# character vector
vect1 <- c('Jack', 'Jill', 'John')           

# 3 x 4 matrix
mat <- matrix(sample(12), nrow = 3)          

# list of 2 objects
list1 <- list(names = vect1, numbers = mat)  
list1

# the [] operator
list1[1]

# use the [[]] operator
list1[[1]]

# test the class
class(list1[1])

class(list1[[1]])

# combine [] and [[]] operators
list1

# returns 'Jack'
list1[[1]][1]                                

# returns 'John'
list1[[1]][3]                                

# returns element in 2nd row/ 3rd column
list1[[2]][2,3]                              

# returns all elements of 3rd column of mat
list1[[2]][, 3]                              

# returns all elements of 3rd row of mat
list1[[2]][3, ]                              


# the $ operator
list1

# extract the vector
list1$names

# extract the matrix
list1$numbers

# returns 'Jack'
list1$names[1]                               

# returns 'John'
list1$names[3]                               

# returns element in 3rd row/ 2nd column
list1$numbers[3, 2]                          

# returns all elements of 3rd row 
list1$numbers[3, ]                           

# returns all elements of 2nd column
list1$numbers[, 2]                           


# add/delete list objects
list1

# logical vector
vect2 <- c(TRUE, FALSE, FALSE, TRUE, FALSE)  

# add object using $ operator
list1$logic <- vect2                         
list1

# 3 x3 matrix
mat2 <- matrix(1:9, ncol = 3, byrow = TRUE)  

# add object using [[]] operator
list1[[4]] <- mat2                           
list1

# replace list elements
# replace vect1 with vect2
list1$names <- vect2                         
list1

# 3 x3 matrix
mat2 <- matrix(1:9, ncol = 3, byrow = TRUE)  

# replace mat1 with mat2
list1[[2]] <- mat2                           
list1

# delete list objects
list1

# delete names vector
list1$names <- NULL

# delete numbers matrix
list1[[2]] <- NULL                           
list1


# dissolving lists
# character vector
vect1 <- c('Jack', 'Jill', 'John')           

# 3 x 4 matrix
mat <- matrix(sample(12), nrow = 3)          

# list of 2 objects
list1 <- list(names = vect1, numbers = mat)  
list1

# disolve the list using the unlist function
unlist(list1)