Count each character and store as <K,V> pair

How can I count the unique characters from a given string and store it as a key - value pair in R programming using the base package? Here key will be the distinct character and value will be the occurrence of the character within the string.

Let's say I have the input string as "hello". The expected output would be:

"hello"

h -> 1
e -> 1
l -> 2
o -> 1


2 Answers
2

We can use table to count the frequencies after we split the string in letters. A simple sapply can convert it to a list if needed, i.e.

table

sapply

table(strsplit('hello', ''))
#e h l o
#1 1 2 1

#or

sapply(table(strsplit('hello', '')), list)
#$`e`
#[1] 1

#$h
#[1] 1

#$l
#[1] 2

#$o
#[1] 1


R does not have any native hashmap support, although there is a hashmap package. However, we can easily enough use a list here to simulate hashing functionality:

hashmap

lst <- list()
for (i in strsplit('hello', '')[[1]]) {
lst[[i]] <- ifelse(is.null(lst[[i]]), 1, lst[[i]] + 1)
}

lst
$h
[1] 1

$e
[1] 1

$l
[1] 2

$o
[1] 1


Demo

Note that now accessing a key in the map just means accessing an entry in the list, e.g. lst$l returns 2, because l occurs twice in the string hello.

lst$l

l

hello

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