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. AC **ABCD** CDBCABCDBC - 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 DABCDDDCCBCDABADBBBBCDBCADCBBBDCAAACACCCBCBCADBDDABBACACBDABAAACCAAAAACCCCBCBCCABABDDADBABDDDCCDDCCC 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!