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    How to Convert List to Vector in R

    How to Convert List to Vector in R

    To convert a list to a vector in R use unlist() function. This function takes a list as one of the arguments and returns a Vector. A list in R is an object consisting of heterogeneous elements meaning can contain elements of different types whereas a vector in R is a basic data structure containing elements of the same data type.

    In this example, first I will create a list and convert it to a vector by using unlist() function. After converting to vector, you can use typeof() function to check its data type.

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    Quick Examples of Convert List to Vector

    Following are quick examples of converting a list to a vector or creating a list from the vector.

    
# Quick Examples

# Convert list to vector
li <- list('A','B','C')
v <- unlist(li)
print(v)
print(typeof(v))

# Convert List of vectors into vector
li <- list(col1 = c(10, 20, 30),                
           col2 = c(1, 40, 3),                    
           col3 = c(30, 20))   
print(li)
v <- unlist(li, use.names=FALSE)
print(v)

# Convert to numeric vector
li <- list('10','20','30')
v <- unlist(li)
v <- as.vector(v,'numeric')
print(v)
typeof(v)

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    1. Create a List

    Use the list() function to create a list object in R. A list is an object capable of holding heterogeneous elements, allowing it to contain items of various types. Consequently, a list can include vectors, dataframe, matrix, and other types of elements.

    
# Create list
li <- list('A','B','C')

li2 <- list(10,20,30)

li3 <- list('A','B','C',10,20,30)

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    2. Convert List to Vector

    Use unlist() function to convert a list to a vector in R. Let's pass the above created list object li as an argument to unlist() function, this returns a vector with each element of the list.

    
# Convert list to vector
v <- unlist(li)
print(v)

    Yields below output. Since we have character elements in a list, it is converted into a character vector.

    
# Output
> print(v)
[1] "A" "B" "C"

    Let's check the data type of the converted list.

    
# Convert list to vector
typeof(v)

    This outputs a type character.

    <a id="h-3-convert-named-list-to-vector"></a>

    3. Convert Named List to Vector

    Let's create a list with a named vector of numeric elements and convert it to a single vector.

    
# Convert List of vectors into vector
li <- list(col1 = c(10, 20, 30),                
           col2 = c(1, 40, 3),                    
           col3 = c(30, 20)) 
print(li)

#  Convert it to vector
v <- unlist(li)
print(v)

    Yields below output. Notice that when you have a list with multiple vectors and unlisting will create a single vector flattened with all elements.

    
# Output
$col1
[1] 10 20 30

$col2
[1]  1 40  3

$col3
[1] 30 20

# Output of converted vector
col11 col12 col13 col21 col22 col23 col31 col32 
   10    20    30     1    40     3    30    20

    Use unlist(li, use.names=FALSE) to ignore names on the vector.

    
# Output
[1] 10 20 30  1 40  3 30 20

    <a id="h-4-convert-list-to-numeric-vector-of-type-double"></a>

    4. Convert List to Numeric Vector of type double

    If you have a vector with numeric elements but as a string, you can use as.vector() function to convert to numeric type after converting list to vector.

    
li <- list('10','20','30')
v <- unlist(li)
v <- as.vector(v,'numeric')
print(v)
typeof(v)

    
# Output
[1] 10 20 30
[1] "double"

    <a id="h-5-convert-multiple-lists-into-vector"></a>

    5. Convert Multiple Lists into Vector

    To convert multiple lists use the c() function to combine the lists and pass this list to unlist() to convert it to a vector.

    
# Create Multiple Lists into Vector
li1 <- list('A','B','C')
li2 <- list('X','Y','Z')
v <- unlist(c(li1,li2))
print(v)

    Yields below output.

    
# Output
[1] "A" "B" "C" "X" "Y" "Z"

    <a id="h-conclusion"></a>

    Conclusion

    In this article, you have learned how to convert a list to a vector in R by using the unlist() function and also learned how to ignore the names on the vector by using a use.names=FALSE param. You can find the complete example from this article at Github R Programming Examples Project.

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    References