Finding consecutive values in a string in R

Question

I am trying to find 3 or more consecutive "a" within the last 10 letters of my data frame string. My data frame looks like this:

V1
aaashkjnlkdjfoin
jbfkjdnsnkjaaaas
djshbdkjaaabdfkj
jbdfkjaaajbfjna
ndjksnsjksdnakns
aaaandfjhsnsjna

I have written this code, however it just gets out the number of consecutive "a" within the whole string. However, I am wanting to do it so it only looks at the last 10 digits and then prints the string where the consecutive "a" are found. The code I have wrote is:

out: [1] 3 

I am wanting my output to look like this:

jbfkjdnsnkjaaaas
djshbdkjaaabdfkj
jbdfkjaaajbfjna

Can anyone help

Answer 1

Using regex, you could do:

grep("(?=.{10}$).*?a{3,}", string, perl = TRUE, value = TRUE)
[1] "jbfkjdnsnkjaaaas" "djshbdkjaaabdfkj" "jbdfkjaaajbfjna" 

---

string <- c("aaashkjnlkdjfoin", "jbfkjdnsnkjaaaas", "djshbdkjaaabdfkj", 
            "jbdfkjaaajbfjna", "ndjksnsjksdnakns", "aaaandfjhsnsjna")

If you have a dataframe and need tosubset it:

subset(df, grepl("(?=.{10}$).*?a{3}",V1, perl = TRUE))
                V1
2 jbfkjdnsnkjaaaas
3 djshbdkjaaabdfkj
4  jbdfkjaaajbfjna