Sort or Order List in R?

How to sort a list in R? Sorting or Ordering a list in R can be done by using lapply() function or using the order() function after converting to a vector using unlist().

In this article, I will explain how to order a list of elements by name or values in R and by applying ascending or descending order.

1. Quick Examples of Sorting List

Following are quick examples of sorting lists by name or values in R.



# Sort list in ascending order
sorted_li <- lapply(li,sort)

# Sort list in descending order
sorted_li <- lapply(li,sort,decreasing=TRUE)

# Sort named list
sorted_li <- li[order(names(li))]

# Unlist and use order()
sorted_li <- li[order(unlist(li),decreasing=TRUE)]

2. R Sort List Values by Ascending

By using lapply() function you can sort the values of the list in R by ascending order, this function takes a list as an argument and the sort keyword. After applying the sort on the list it returns the ordered list. This by default sorts in ascending order, you can also force it by using decreasing=FALSE argument.

If you have characters in the list, you will see a resultant list in alphabetically sorted order.


# Create list
li <- list(c(5,3,1,2,9,7))

# Sort list in ascending order
sorted_li <- lapply(li,sort)
sorted_li

# Output
#[[1]]
#[1] 1 2 3 5 7 9

3. R Sort List in Descending

Similarly, use decreasing=TRUE to lapply() function to sort a list in descending order in R. If you have a character in the list, it sort Z to A (reverse alphabetical order).


# Sort list in descending order
sorted_li <- lapply(li,sort,decreasing=TRUE)
sorted_li

# Output
#[[1]]
#[1] 9 7 5 3 2 1

4. Sort List by Name

To sort list by name in R, first, let’s create the named list and use the order() function to sort. Note that when you sort by name using order() it sorts names but not the values.


# Create named list
li <- list(B = c(5,3,1,2,9,7),
           A = c(4,7,9,1,3,5),
           C = c(2,8,4,6,1,4))
li

# Sort named list
sorted_li <- li[order(names(li))]
sorted_li

Yields below output.

r sort list descending

4. Sort List of List

To sort the complex list of list data structure use order() and apply() functions together. In my example, each sublist contains an integer and a character string, I will order the lists such that the final list is sorted by the integers in ascending order.


# Sort list of list
A <- list(1,"Java")
B <- list(5, "Python")
C <- list(6, "R")
D <- list(2, "PHP")

li <- list(A,B,C,D)
li

# Sort list of list
sorted_li <- li[order(sapply(li,'[[',1))]
sorted_li

I will leave this to you to run and explore the output.

6. Sort List by after unlist()

You can also sort lists by first unlist into vectors and using the order() function. The below example sorts the list in descending order.


# Unlist and use order()
li <- setNames(list(5,3,1,2,9,7),1:6)
sorted_li <- li[order(unlist(li),decreasing=TRUE)]
sorted_li

5. Conclusion

In this article, you have learned how to sort or order a list in R by name, value, and by ascending, and descending order. Also learned how to sort list of list and by using unlist to vector.

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References

NNK

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