Question

Given a list, I seek to create a new list with duplicate list entries removed but also wish to store the multiplicity of each unique list entry.

For example, in the following list, I would like to obtain a list of three elements: character(0), “11”, “33” “44” and their corresponding multiplicities of 2, 2 and 1, respectively:

> list

[[1]]

character(0)

[[2]]

"11" 

[[3]]

"11" 

[[4]]

character(0)

[[5]]

"33" "44"

Answer 1

You can use unique to get the unique entries and table with match to get the frequencies:

#create list
l <- list(character(0),"11","11",character(0),c("33","44"))

#unique elements
ul <- unique(l)
ul
[[1]]
character(0)

[[2]]
[1] "11"

[[3]]
[1] "33" "44"

#get frequencies
table(match(l,ul))

1 2 3 
2 2 1