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:
We use the
readLines()
function to read all input lines from stdin.We iterate over each line using a for loop.
The
str_to_upper()
function from thestringr
package is used to convert each line to uppercase.We use
cat()
to print the uppercase line, adding a newline character.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.