Longest Line

April 18, 2017

We begin with a Scheme solution, since that is the primary language of this blog:

(define (longest-line file-name)
  (with-input-from-file file-name
    (lambda ()
      (let loop ((line (read-line))
                 (max-len 0) (max-line ""))
        (cond ((eof-object? line) max-line)
              ((< max-len (string-length line))
                (loop (read-line) (string-length line) line))
              (else (loop (read-line) max-len max-line)))))))

I’ve spent a lot of time programming in Awk, so this solution popped quickly into my mind:

awk ' length > max_length {
          max_length = length
          longest_line = $0 }
      END { print longest_line } ' < filename

That’s written for clarity; in real life, at an interactive command prompt, I would probably write it like this:

awk 'length>m{m=length;l=$0} END{print l}' <filename

My third solution combines standard unix tools:

cat filename |
  awk '{print length, $0}' |
  sort -n |
  tail -1 |
  sed 's/[0-9]* //'

Here’s my fourth solution; I’ll leave it to you figure out how it works:

sed -rn "/.{$(expand -t1 filename | wc -L)}/p" filename

You can run the Scheme version of the program at http://ideone.com/8jNtqJ.

Pages: 1 2

Posted by programmingpraxis
Filed in Exercises
4 Comments »

4 Responses to “Longest Line”

  1. Rutger said
    April 18, 2017 at 10:41 AM

    Option 1:
    wc -L filename

    Option 2:

    def longest_line(filename):
	line, length = "", -1
	with open(filename, 'r') as file_handler:
	    for l in file_handler:
	    	if len(l) > length:
	    		line, length = l, len(l)
	return line, length
  2. Paul said
    April 18, 2017 at 11:48 AM 
    def longest_line(fname, encoding="UTF-8"):
    with open(fname, encoding=encoding) as f:
        return max((line for line in f), key=len)

def longest_silly(fname, encoding="UTF-8"):
    line = ""
    with open(fname, encoding=encoding) as f:
        txt = f.read()
        pos, length = 0, -1
        ind = txt.find("\n")
        while ind > -1:
            if ind - pos > length:
                length, line = ind - pos, txt[pos:ind]
            pos = ind+1
            ind = txt.find("\n", pos)
    return line
  3. john said
    April 19, 2017 at 1:09 AM

    Here are two solutions: Perl 5 and C11. They both expect filenames to be passed as command line arguments (- for stdin).

    The Perl solution:

    #!/usr/bin/env perl
    my $longest = "\n";

    while (<>) {
        $longest = $_ if (length($longest) < length);
    }

    print "length: " . length($longest) . "\n";
    print "longest: " . $longest;

    The C11 solution:

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>

    int main(int argc, char **argv) {
      const size_t max_line_length = 1024;

      char *filename;
      FILE *fp;
      char line[max_line_length];
      char longest[max_line_length];

      int err;

      longest[0] = '\0';
      
      for (int i = 1; i < argc; ++i) {
        filename = argv[i];
        
        if (strcmp(filename, "-") == 0) {
          fp = stdin;
        } else {
          fp = fopen(filename, "r");
          if (fp == NULL) {
            perror(filename);
            continue; // ignore bad files
          }
        }

        while (fgets(line, max_line_length, fp) != NULL) {
          if (strlen(line) > strlen(longest)) {
            (void)memcpy(longest, line, max_line_length);
          }
        }

        if (!feof(fp)) {
          err = fprintf(stderr, "There was an error while reading %s.\n", filename);
          if (err < 0) {
            exit(1);
          }
        }
      }

      printf("length: %zd\n", strlen(longest));
      printf("longest: %s", longest);

      exit(0);
    }

  4. James Curtis-Smith said
    April 19, 2017 at 11:06 AM

    Returning all the longest lines in perl

      my @L = (q());
  while(<>) {
    next if length $L[0] > length $_;
    @L = () if length $L[0] < length $_;
    push @L, $_;
  }
  return @L;
}

    or you can do it with bash

    x=''
z=0
while read l
do
  if [ $z -lt ${#l}
  then
    x=$l;z=${#l};
 fi
 done
 echo $x

Leave a comment