Speed up a function that checks for a sequence

Question

I created a function yes.seq that takes two arguments, a pattern pat and data dat, the function looks for the presence of a pattern in the data and in the same sequence.

For example:

dat <- letters[1:10]
dat
[1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
pat <- c('a',"c","g")
 
 yes.seq(pat = pat,dat = dat)
[1] TRUE

because this sequence is in the pattern and in the same order.

"a" "b" "c" "d" "e" "f" "g" "h" "i" "j"

If, for example, we reverse the pattern, then we get FALSE:

yes.seq(pat = pat,dat =  **rev(dat)**   )
[1] FALSE

Here is my function:

yes.seq <- function(pat , dat){  
  lv <- rep(F,length(pat))
  k <- 1     
  for(i in 1:length(dat)){        
            if(dat[i] == pat[k]) 
              {
              lv[k] <- TRUE
              k <- k+1 
              }       
    if(k==length(pat)+1) break
  }
  return(  all(lv)   )
}

I am not satisfied with the speed of this function. Can you help me with that?

Answer 1

Here is a vectorized version:

yes.seq <- function(dat, pat) {
  paste(dat[dat %in% pat], collapse = "") == paste(pat, collapse = "")
}

yes.seq(dat, pat)
# [1] TRUE
yes.seq(dat, rev(pat))
# [1] FALSE