R: Working with lists

Lists in R allow you to store data of different types into a single data structure. While they are extremely useful, they can be a bit confusing to work with at first.

Let’s start by creating a list. The syntax is simple enough, just add list() around the elements you want to put in your list.

l1 <- list(24, c(12,15,19), "Dogs")
l1

Here is the output. Note we have 3 different groupings. 1 number, 1 vector (with 3 elements) and 1 character

2016-12-05_14-20-32.jpg

You can call on each element using the element names (found in the double brackets [[]])

l1[[2]]
l1[[1]]

Here are the results

2016-12-05_14-26-55

Now, what if you want to call 1 element from the vector in [[2]]

You do this by adding [] to the end of the line

l1[[2]][3]

This will give you the 3rd number in the vector found in [[2]]

2016-12-05_14-27-10

To make it easier to work with lists, you can rename the elements.

names(l1)  # shows NULL since the elements have no names
names(l1) = c("Number", "Vector", "Char")
names(l1) # now shows assigned names

 

Now you can call on the list using the names.

l1$Char # will return "Dogs"

l1$Vector[2] #will return the second number in the vector in the list

You can also simply name your elements when creating your list

rm(l1) #deletes list
l1 <- list(Number=24,Vector = c(12,15,19), Char="Dogs")

You can add a new element to you list via number

l1[[4]] = "New Element"

Even better, you can add via new name

l1$Char2 <- "Cat"

Now let’s look at our list

2016-12-05_14-42-47.jpg

Now we can use the names() function to give element 4 a name, or we can just get rid of it.

To delete an elements, use NULL

l1[[4]] <- NULL

Now the last thing we will cover is how to subset a list

l1[1:3] # gives us elements 1 -3

2016-12-05_14-50-32.jpg

We want to pick some elements out of order

l1[c(2,4)]
l1[c("Number","Char")]

2016-12-05_14-51-56

 

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