Line Filters in R Programming Language

Our line filter program reads input from stdin, processes it, and then prints a derived result to stdout. In this case, it will write a capitalized version of all input text. You can use this pattern to write your own R line filters.

# Load necessary libraries
library(stringr)

# Main function
main <- function() {
  # Read input lines from stdin
  input_lines <- readLines("stdin")
  
  # Process each line
  for (line in input_lines) {
    # Convert the line to uppercase
    uppercase_line <- str_to_upper(line)
    
    # Print the uppercase line
    cat(uppercase_line, "\n", sep = "")
  }
  
  # Check for errors during input reading
  if (length(warnings()) > 0) {
    cat("error:", warnings(), file = stderr())
    quit(status = 1)
  }
}

# Run the main function
main()

In this R version:

1. We use the readLines() function to read all input lines from stdin.

2. We iterate over each line using a for loop.

3. The str_to_upper() function from the stringr package is used to convert each line to uppercase.

4. We use cat() to print the uppercase line, adding a newline character.

5. After processing all lines, we check for any warnings that occurred during input reading. If there were warnings, we print them to stderr and exit with a status code of 1.

To try out our line filter, first make a file with a few lowercase lines:

$ echo 'hello'   > /tmp/lines
$ echo 'filter' >> /tmp/lines

Then use the line filter to get uppercase lines:

$ cat /tmp/lines | Rscript line_filter.R
HELLO
FILTER

This R script provides similar functionality to the original Go program, reading input line by line, converting each line to uppercase, and writing the result to stdout.