 # R List

In this tutorial, we will learn about list in R with the help of examples.

A List is a collection of similar or different types of data.

In R, we use the `list()` function to create a list. For example,

``````# list with similar type of data
list1 <- list(24, 29, 32, 34)

# list with different type of data
list2 <- list("Ranjy", 38, TRUE)``````

Here,

• list1 - list of integers
• list2 - list containing string, integer, and boolean value

## Access List Elements in R

In R, each element in a list is associated with a number. The number is known as a list index.

We can access elements of a list using the index number (1, 2, 3 …). For example,

``````list1 <- list(24, "Sabby", 5.4, "Nepal")

# access 1st item
print(list1) # 24

# access 4th item
print(list1) # Nepal``````

In the above example, we have created a list named list1.

Here, we have used the vector index to access the vector elements

• `list1` - access the first element 24
• `list1` - accesses the third element `"Nepal"`

Note: In R, the list index always starts with 1. Hence, the first element of a list is present at index 1, second element at index 2 and so on.

## Modify a List Element in R

To change a list element, we can simply reassign a new value to the specific index. For example,

``````list1 <- list(24, "Sabby", 5.4, "Nepal")

# change element at index 2
list1 <- "Cathy"

# print updated list
print(list1)``````

Output

```[]
 24

[]
 "Cathy"

[]
 5.4

[]
 "Nepal"```

Here, we have reassigned a new value to index 2 to change the list element from `"Sabby"` to `"Cathy"`.

## Add Items to R List

We use the `append()` function to add an item at the end of the list. For example,

``````list1 <- list(24, "Sabby", 5.4, "Nepal")

# using append() function
append(list1, 3.14)``````

Output

```[]
 24

[]
 "Sabby"

[]
 5.4

[]
 "Nepal"

[]
 3.14```

In the above example, we have created a list named list1. Notice the line,

``append(list1, 3.14)``

Here, `append()` adds 3.14 at the end of the list.

## Remove Items From a List in R

R allows us to remove items for a list. We first access elements using a list index and add negative sign `-` to indicate we want to delete the item. For example,

• `[-1]` - removes 1st item
• `[-2]` - removes 2nd item and so on.
``````list1 <- list(24, "Sabby", 5.4, "Nepal")

# remove 4th item
print(list1[-4]) # Nepal``````

Output

```[]
 "Sabby"

[]
 5.4

[]
 "Nepal"```

Here, `list[-4]` removes the 4th item of list1.

## Length of R List

In R, we can use the `length()` function to find the number of elements present inside the list. For example,

``````list1 <- list(24, "Sabby", 5.4, "Nepal")

# find total elements in list1 using length()
cat("Total Elements:", length(list1))``````

Output

`Total Elements: 4`

Here, we have used the `length()` function to find the length of list1. Since there are 4 elements in list1 so `length()` returns 4.

## Loop Over a List

In R, we can also loop through each element of the list using the for loop. For example,

``````items <- list(24, "Sabby", 5.4, "Nepal")

# iterate through each elements of numbers
for (item in items) {
print(item)
}``````

Output

``` 24
 "Sabby"
 5.4
 "Nepal"```

## Check if Element Exists in R List

In R, we use the `%in%` operator to check if the specified element is present in the list or not and returns a boolean value.

• `TRUE` - if specified element is present in the list
• `FALSE` - if specified element is not present in the list

For example,

``````list1 <- list(24, "Sabby", 5.4, "Nepal")

"Sabby" %in% list1 # TRUE

"Kinsley" %in% list1 # FALSE``````

Output

```TRUE
FALSE```

Here,

• `"Larry"` is present in list1, so the method returns `TRUE`
• `"Kinsley"` is not present in list1, so the method returns `FALSE`