Use LaF and grepl together

Question

I would like to read in a possibly large text file and filter the relevant lines on the fly based on a regular expression. My first approach was using the package LaF which supports chunkwise reading and then grepl to filter. However, this seems not to work:

library(LaF)
fh <- laf_open_csv("myfile.txt", column_types="string", sep="°") 
# would be nice to declare *no* separator
fh[grepl("abc", fh[[1]]), ]

returns an error in as.character.default(x) -- no method to convert this S4 to character. It seems like grepl is applied to the S4 function and not to the chunks.

Is there a nice way to read text lines from a large file and filter them selectively?

Answer 1

OK, I just discovered process_blocks:

regfilter <- function(df, result) c(result, df[grepl("1745", df[[1]]),1])
process_blocks(fh, regfilter)

This works, now I only need to find a way to ignore separators..