How to calculate percentage of each characters from whole variable strings?

Here is dummy datasets:

a <- c("CC", "CCAA", "ABB")   
id <- c("a", "b", "c")    
data <- data.frame(id, a)
head(data)
#  id    a
#1  a   CC
#2  b CCAA
#3  c  ABB

And we can calculate percentage of the each string presented in the rows

library(data.table)
data1 <- setDT(data)[, .N, .(a)][, perc := N/sum(N), .()][]
head(data1)
#       a N      perc
# 1:   CC 1 0.3333333
# 2: CCAA 1 0.3333333
# 3:  ABB 1 0.3333333

But, How to calculate percentage of each characters from whole "a" variable strings?

# [Expected output]   
#              a  N   perc
# 1:           A  3   0.33
# 2:           B  2   0.22
# 3:           C  4   0.44 

R base and tidyverse approach more preferred.

>Solution :

tidyverse option –

library(tidyverse)

data %>%
  mutate(a = str_split(a, "")) %>%
  unnest_longer(a) %>%
  count(a, name = "N") %>%
  mutate(perc = prop.table(N))

# A tibble: 3 × 3
#   a         N  perc
#  <chr> <int> <dbl>
#1 A         3 0.333
#2 B         2 0.222
#3 C         4 0.444

Base R –

a1 <- strsplit(data$a, "") |> unlist()
a2 <- table(a1)
a3 <- prop.table(a2)

data.frame(a = names(a2), 
           N = as.integer(a2), 
           perc = as.numeric(a3))

#  a N      perc
#1 A 3 0.3333333
#2 B 2 0.2222222
#3 C 4 0.4444444