What are the differences between vector and list data types in R?
ListRVectorList Problem Overview
What are the main differences between vector and list data types in R? What are the advantages or disadvantages of using (or not) these two data types?
I would appreciate seeing examples that demonstrate the use cases of the data types.
List Solutions
Solution 1 - List
Technically lists are vectors, although very few would use that term. "list" is one of several modes, with others being "logical", "character", "numeric", "integer". What you are calling vectors are "atomic vectors" in strict R parlance:
aaa <- vector("list", 3)
is.list(aaa) #TRUE
is.vector(aaa) #TRUE
Lists are a "recursive" type (of vector) whereas atomic vectors are not:
is.recursive(aaa) # TRUE
is.atomic(aaa) # FALSE
You process data objects with different functions depending on whether they are recursive, atomic or have dimensional attributes (matrices and arrays). However, I'm not sure that a discussion of the "advantages and disadvantages" of different data structures is a sufficiently focused question for SO. To add to what Tommy said, besides lists being capable of holding an arbitrary number of other vectors there is the availability of dataframes which are a particular type of list that has a dimensional attribute which defines its structure. Unlike matrices and arrays which are really folded atomic objects, dataframes can hold varying types including factor types.
There's also the caveat that the is.vector
function will return FALSE
when there are attributes other than names. See: https://stackoverflow.com/questions/11591924/what-is-vector
Solution 2 - List
Lists are "recursive". This means that they can contain values of different types, even other lists:
x <- list(values=sin(1:3), ids=letters[1:3], sub=list(foo=42,bar=13))
x # print the list
x$values # Get one element
x[["ids"]] # Another way to get an element
x$sub$foo # Get sub elements
x[[c(3,2)]] # Another way (gets 13)
str(x) # A "summary" of the list's content
Lists are used in R to represent data sets: the data.frame
class is essentially a list where each element is a column of a specific type.
Another use is when representing a model: the result from lm
returns a list that contains a bunch of useful objects.
d <- data.frame(a=11:13, b=21:23)
is.list(d) # TRUE
str(d)
m <- lm(a ~ b, data=d)
is.list(m) # TRUE
str(m)
Atomic vectors (non-list like, but numeric, logical and character) are useful since all elements are known to have the same type. This makes manipulating them very fast.
Solution 3 - List
As someone who's just gotten into R, but comes from a C/Java/Ruby/PHP/Python background, here's how I think of it.
A list
is really an array + a hashmap. It's a PHP associative array.
> foo = list(bar='baz')
> foo[1]
'baz'
> foo$bar
'baz'
> foo[['bar']]
'baz'
A vector
is a fixed-type array/list. Think of it like a linked list - because putting dissimilar items into a linked list is an anti-pattern anyways. It's a vector in the same sense that SIMD/MMX/vector units use the word.
Solution 4 - List
This and similar introductory questions are answered in http://www.burns-stat.com/pages/Tutor/hints_R_begin.html
It is meant to be a gentle introduction that gets you up and running with R as quickly as possible. To some extent it succeeds.
--- Edit: --
An attempt to explain further; quoted from the above reference.
> Atomic vector > > There are three varieties of atomic vector that you are likely to > encounter: > > - “numeric” > - “logical” > - “character” > > The thing to remember about atomic vectors is that all of the elements > in them are only of one type. > > List > > Lists can have different types of items in different components. A > component of a list is allowed to be another list , an atomic vector > (and other things).
Please also refer to this link.
Solution 5 - List
list include multiple data types like character, numeric, logical et. but vector only contains similar type of data. for ex:
scores <- c(20,30,40,50)
student <- c("A","B","C","D")
sc_log <- c(TRUE,FALSE,FALSE,TRUE)
for list:
mylist <- list(scores,student,sc_log)
# search for class of mylist vector
#check structure of mylist using str() function.
str(mylist)
[1] list of 3
[1] $:num [1:4] 20 30 40 50
[2] $:chr [1:4] "A""B""C""D"
[3] $:log [1:4] TRUE FALSE FALSE TRUE
which means list containing multiple data types like numeric, character and logical in mylist.But in vector there will be single data type of all elements in that vector
for ex:
for vector:
vector1 <- c(1,2,3,4)
Class(vector1)
[1] "Numeric"
#which means all elements of vector containing single data type that is numeric only.