Regular expressions (RegEx) and dplyr::filter()

Question

I have a simple data frame that looks like this:

x <- c(\"aa\", \"aa\", \"aa\", \"bb\", \"cc\", \"cc\", \"cc\")
y <- c(101, 102, 113, 201, 202, 344, 40         


        

Answer 1

You need to double check the documentations for grepl and filter.

For grep/grepl you have to also supply the vector that you want to check in (y in this case) and filter takes a logical vector (i.e. you need to use grepl). If you want to supply an index vector (from grep) you can use slice instead.

df %>% filter(!grepl("^1", y))

Or with an index derived from grep:

df %>% slice(grep("^1", y, invert = TRUE))

But you can also just use substr because you are only interested in the first character:

df %>% filter(substr(y, 1, 1) != 1)

Answer 2

With a combination of dplyrand stringr (to stay within the tidyverse), you could do :

df %>% filter(!str_detect(y, "^1"))

This works because str_detect returns a logical vector.