Create word variations in R

Question

I have an assigment in which I have absolutely no idea how to start to make it work.

I have to create variations of list of words, where will be replaced every character (between 1st and last) with '*' on different positions.

It should look something like this:

input: c('smog', 'sting')

desired output: 's*og', 'sm*g', 's**g', 's*ing', 'st*ng', 'sti*g', 's***g'

Any idea how to achieve something like this?

Thank you very much

UPDATE I've found this solution:

s <- c( 'smog')
f <- function(x,y) {substr(x,y,y) <- "*"; x}
g <- function(x) Reduce(f,x,s)
unlist(lapply(1:(nchar(s)-2),function(x) combn(2:(nchar(s)-1),x,g)))

output:
[1] "s*og" "sm*g" "s**g"

the only problem with this is, that it works only when there is one word in the string, not several

Answer 1

See also this SO post for related techniques: Create all combinations of letter substitution in string

EDIT

From the OP edit and comment:

repfun2 <- function(s){
  f <- function(x,y) {substr(x,y,y) <- "*"; x}
  g <- function(x) Reduce(f,x,s)
  out <- unlist(lapply(1:(nchar(s)-2),function(x) combn(2:(nchar(s)-1),x,g)))
  return(out)
}
lapply(test2, FUN = repfun2)

Ouput:

> lapply(test2, FUN = repfun2)
[[1]]
[1] "s*og" "sm*g" "s**g"

[[2]]
[1] "s*ing" "st*ng" "sti*g" "s**ng" "s*i*g" "st**g" "s***g"

---

Previous answer for random replacement

I understand you want a random replacement of characters in a vector of strings. If this is correct, here is an idea:

test2 <- c('smog', 'sting')

repfun <- function(.string) {
  n_char <- nchar(.string)
  # random selection of n characters that will be replaced in the string
  repchar <- sample(1:n_char, size = sample(1:n_char, size = 1))
  # replacing the characters in the string
  for(i in seq_along(repchar)) substring(.string, repchar[i], repchar[i]) <- "*"
  return(.string)
}
lapply(test2, FUN = repfun)

Some outputs:

> lapply(test2, FUN = repfun)
[[1]]
[1] "*mog"

[[2]]
[1] "s*ing"

> lapply(test2, FUN = repfun)
[[1]]
[1] "s*o*"

[[2]]
[1] "s*i*g"

The basic idea is:

1. Determine the number of characters in a string,
2. Randomly sample it based on its length,
3. Replace the randomly sampled characters by "*"
4. Use lapply to pass a vector of character strings.

I think you can improve it by removing the for loop if needed, see some ideas here and here