R: Introducing a WHILE LOOP to a Function-CodePudding

I am working with the R programming language.

I am trying to count the first time a certain pattern (e.g. ABCD) appears in a random string (e.g. ACABCDCDBCABCDBC - answer =6 ). I wrote a function to do this:

library(stringr)

letters <- c("A", "B", "C", "D")

results <- list()
for (i in 1:100)
    
{
    
    iteration_i = i
    letters_i = paste(sample(letters, 100, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25)),collapse="")
    position_i = str_locate(letters_i, "ADBC") 
    
    results_tmp = data.frame(iteration_i , letters_i, position_i)
    
    results[[i]] <- results_tmp
    
}

results_df <- do.call(rbind.data.frame, results)

This looks something like this now (note: I don't think this is correct - in row 5, I see ABCD at the beginning of the row, but its being recorded as NA for some reason):

  iteration_i                                                                                            letters_i start end
1           1 BACDCCCDCCCDCDDBBCBBAACACBBBBAAABDDDACAABDDABBABADCDDCDACCBBBCABCDABCDCCCDADDDBADBDCADAABDBDCDCAACCB    NA  NA
2           2 CACACCCCDCCBADACBBAADBCABBAAAAADBDDBCADCAAADADAAABDCABBAABABBCBDADCDDDDCDBADDBDCBCDDDBDCDDAACBBBBACA    20  23
3           3 CDCBDAABDDDDADBAAABBADAADBDDDBDADDCABADDDCDABBBCBCBBACBBDADABBCDCCACDBCDCDDBDBADBCDCADDADDDBDBAAABBD    79  82
4           4 ADBCDBADADBAAACAADACACACACBDDCACBDACCBDAAABDBAAAABBCCDBADADDADCBCABCBAABDCBCDCDACDCCDBADCBDDAADBCDAC     1   4
5           5 D**ABCD**DDCCBCDABADBBBBCDBCADCBBBDCAAACACCCBCBCADBDDABBACACBDABAAACCAAAAACCCCBCBCCABABDDADBABDDDCCDDCCC    NA  NA
6           6 DDDDDBDDDDBDDDABDDADAADCABCDAABBCCCDAABDDAACBDABBBBBABBCBDADBDCCAAADACCBCDDBDCAADCBBBCACDBBADDDDCABC    NA  NA

Currently, I am only generating 100 letters and hoping that this is enough to observe the desired pattern (sometimes this doesn't happen, notice the NA's) - is there a way to add a WHILE LOOP to what I have written to keep generating letters until the desired pattern first appears?

Can someone please show me how to do this?

Thanks!

CodePudding user response：

The loop is a repeat loop, not while, that only breaks when the pattern is found. I have set the results list length to 2, there's no point in making it bigger just to test the code.

library(stringr)

Letters <- c("A", "B", "C", "D")
Pattern <- "ADBC"
n <- 2L

set.seed(2022)

results <- vector("list", length = n)
for (i in seq.int(n)) {
  repeat {
    l <- sample(Letters, 100, replace = TRUE, prob=c(0.25, 0.25, 0.25, 0.25))
    letters_i <- paste(l, collapse = "")
    position_i <- str_locate(letters_i, pattern = Pattern)
    if(any(!is.na(position_i))) break
  }
  results_tmp <- data.frame(iteration = i, letters = letters_i, position_i)
  
  results[[i]] <- results_tmp
}

results_df <- do.call(rbind.data.frame, results)
results_df
#>   iteration                                                                                              letters start end
#> 1         1 ADBDBDBBCABBBDDBADDAADCBBADACACDCCBBADAADCDDABADCABCDCDDCCCBDDAABACCBDAAAADBDDCCCCADBCBBDABBDCCCBADD    83  86
#> 2         2 DDBDBDBCDDBDBBBDBABBCCBBCCBDBDABBAAABACABADCCBBABADBCCCDABABBDBADCADCABDDDAAACCBDCAACACACBBDDDACCDDC    50  53

^{Created on 2022-06-11 by the reprex package (v2.0.1)}