R Lists
Lists
A list in R can contain many different data types inside it. A list is a collection of data which is ordered and changeable.
To create a list, use the list() function:
Example
# List of strings
thislist <- list("apple", "banana", "cherry")
# Print the list
thislist
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Access Lists
You can access the list items by referring to its index number, inside brackets. The first item has index 1, the second item has index 2, and so on:
Change Item Value
To change the value of a specific item, refer to the index number:
Example
thislist <- list("apple", "banana", "cherry")
thislist[1] <- "blackcurrant"
# Print the updated list
thislist
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List Length
To find out how many items a list has, use the length() function:
Check if Item Exists
To find out if a specified item is present in a list, use the %in% operator:
Example
Check if "apple" is present in the list:
thislist <- list("apple", "banana", "cherry")
"apple" %in% thislist
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Add List Items
To add an item to the end of the list, use the append() function:
Example
Add "orange" to the list:
thislist <- list("apple", "banana", "cherry")
append(thislist,
"orange")
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To add an item to the right of a specified index, add "after=index number" in the append() function:
Example
Add "orange" to the list after "banana" (index 2):
thislist <- list("apple", "banana", "cherry")
append(thislist,
"orange", after = 2)
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Remove List Items
You can also remove list items. The following example creates a new, updated list without an "apple" item:
Example
Remove "apple" from the list:
thislist <- list("apple", "banana", "cherry")
newlist <- thislist[-1]
# Print the new list
newlist
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Range of Indexes
You can specify a range of indexes by specifying where to start and where to end the range, by using the :
operator:
Example
Return the second, third, fourth and fifth item:
thislist <- list("apple", "banana", "cherry", "orange", "kiwi", "melon",
"mango")
(thislist)[2:5]
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Note: The search will start at index 2 (included) and end at index 5 (included).
Remember that the first item has index 1.
Loop Through a List
You can loop through the list items by using a for loop:
Example
Print all items in the list, one by one:
thislist <- list("apple", "banana", "cherry")
for (x in thislist) {
print(x)
}
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Join Two Lists
There are several ways to join, or concatenate, two or more lists in R.
The most common way is to use the c() function, which combines two elements together:
Example
list1 <- list("a", "b", "c")
list2 <- list(1,2,3)
list3 <-
c(list1,list2)
list3
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