Lists

A list is one of R’s most flexible data types.

Lists are similiar to vectors except that:

Example: Create a New List Object

To create a list, use list():

## Make a list from scratch
buff_data <- list(id = "toni", 
                  species = "buffalo", 
                  age = 12, 
                  sex = "female", 
                  treatment = TRUE, 
                  wt = 182, 
                  tested = c(2013, 2014, 2016),
                  herd = c("west", "hilltop"))
class(buff_data)
buff_data

## [1] "list"
## $id
## [1] "toni"
## 
## $species
## [1] "buffalo"
## 
## $age
## [1] 12
## 
## $sex
## [1] "female"
## 
## $treatment
## [1] TRUE
## 
## $wt
## [1] 182
## 
## $tested
## [1] 2013 2014 2016
## 
## $herd
## [1] "west"    "hilltop"

Grabbing Elements from a List

There are multiple ways you can get elements from a list:

## Get individual elements from a list
buff_data$id
buff_data[[4]]
buff_data[["tested"]]

## [1] "toni"
## [1] "female"
## [1] 2013 2014 2016

names(buff_data)

## [1] "id"        "species"   "age"       "sex"       "treatment" "wt"        "tested"    "herd"

names(buff_data)[4] <- "gender"

Nested Lists

If a list element is a vector (or another list), you can keep adding square brackets:

buff_data$tested[2]

## [1] 2014

buff_data[ c(3,5)]

## $age
## [1] 12
## 
## $treatment
## [1] TRUE

Modifying Lists

Updating an element

To change a list element, you simply give it a new value (just like a vector):

buff_data$selected <- FALSE
buff_data$selected

## [1] FALSE

Adding an element

To add a list element, assign a new value to an element as if it was already there, and R will add it ‘on the fly’.

buff_data$mother <- "luci"

Deleting an element

To delete a list element, set it to NULL.

buff_data$herd <- NULL
names(buff_data)

## [1] "id"        "species"   "age"       "gender"    "treatment" "wt"        "tested"    "selected"  "mother"

Merging lists

You can join two lists together with c():

more_meas <- list(diet_supplement = TRUE,
                  vaccinated = c(FALSE, FALSE, FALSE, TRUE))

c(buff_data, more_meas)

## $id
## [1] "toni"
## 
## $species
## [1] "buffalo"
## 
## $age
## [1] 12
## 
## $gender
## [1] "female"
## 
## $treatment
## [1] TRUE
## 
## $wt
## [1] 182
## 
## $tested
## [1] 2013 2014 2016
## 
## $selected
## [1] FALSE
## 
## $mother
## [1] "luci"
## 
## $diet_supplement
## [1] TRUE
## 
## $vaccinated
## [1] FALSE FALSE FALSE  TRUE

Converting a list to a vector

You can convert a list back to a vector with unlist().

R will do its best to convert all the list elements to a common data type (probably character if they’re mixed), and returned a named vector.

unlist(buff_data)

##        id   species       age    gender treatment        wt   tested1   tested2   tested3  selected    mother 
##    "toni" "buffalo"      "12"  "female"    "TRUE"     "182"    "2013"    "2014"    "2016"   "FALSE"    "luci"

S3 and S4 Objects

Lists are also referred to as ‘S3’ objects.

‘S4’ objects are newer - like ‘super lists’.