Kernighans large earthquake problem: Difference between revisions

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<pre>
<pre>
8/27/1883 Krakatoa 8.8
8/27/1883 Krakatoa 8.8
5/18/1980 MountStHelens 7.6
5/18/1980 MountStHelens 7.6
</pre>
</pre>


Revision as of 06:37, 15 June 2018

Task
Kernighans large earthquake problem
You are encouraged to solve this task according to the task description, using any language you may know.

Brian Kernighan, in a lecture at the University of Nottingham, described a problem on which this task is based.

Problem

You are given a a data file of thousands of lines; each of three `whitespace` separated fields: a date, a one word name and the magnitude of the event.

Example lines from the file would be lines like: 

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6
3/13/2009    CostaRica           5.1
Task
  1. Create a program or script invocation to find all the events with magnitude greater than 6
  2. Assuming an appropriate name e.g. "data.txt" for the file:
    1. Either: Show how your program is invoked to process a data file of that name.
    2. Or: Incorporate the file name into the program, (as it is assumed that the program is single use).

ALGOL 68

<lang algol68>IF FILE input file; 

   STRING file name = "data.txt";
   open( input file, file name, stand in channel ) /= 0

THEN 

   # failed to open the file #
   print( ( "Unable to open """ + file name + """", newline ) )

ELSE 

   # file opened OK #
   BOOL at eof := FALSE;
   # set the EOF handler for the file #
   on logical file end( input file, ( REF FILE f )BOOL:
                                    BEGIN
                                        # note that we reached EOF on the latest read #
                                        at eof := TRUE;
                                        # return TRUE so processing can continue #
                                        TRUE
                                    END
                      );
   # return the real value of the specified field on the line #
   PROC real field = ( STRING line, INT field )REAL:
        BEGIN
           REAL result  := 0;
           INT  c pos   := LWB line;
           INT  max pos := UPB line;
           STRING f     := "";
           FOR f ield number TO field WHILE c pos <= max pos DO
               # skip leading spaces #
               WHILE IF c pos > max pos THEN FALSE ELSE line[ c pos ] = " " FI DO
                   c pos +:= 1
               OD;
               IF c pos <= max pos THEN
                   # have a field #
                   INT start pos = c pos;
                   WHILE IF c pos > max pos THEN FALSE ELSE line[ c pos ] /= " " FI DO
                       c pos +:= 1
                   OD;
                   IF field number = field THEN
                       # have the required field #
                       f := line[ start pos : c pos - 1 ]
                   FI
               FI
           OD;
           IF f /= "" THEN
               # have the field - assume it a real value and convert it #
               FILE real value;
               associate( real value, f );
               on value error( real value
                             , ( REF FILE f )BOOL:
                                    BEGIN
                                        # "handle" invalid data #
                                        result := 0;
                                        # return TRUE so processing can continue #
                                        TRUE
                                    END
                             );
               get( real value, ( result ) )
           FI;
           result
        END # real field # ;
   # show the lines where the third field is > 6 #
   WHILE NOT at eof
   DO
       STRING line;
       get( input file, ( line, newline ) );
       IF real field( line, 3 ) > 6 THEN
           print( ( line, newline ) )
       FI
   OD;
   # close the file #
   close( input file )

FI</lang>

AWK

<lang awk> awk '$3 > 6' data.txt</lang>

C++

<lang c++>// Randizo was here!

  1. include <iostream>
  2. include <fstream>
  3. include <string>

using namespace std;

int main() { 

   ifstream file("../include/earthquake.txt");

   int count_quake = 0;
   int column = 1;
   string value;
   double size_quake;
   string row = "";



   while(file >> value)
   {
       if(column == 3)
       {
           size_quake = stod(value);

           if(size_quake>6.0)
           {
               count_quake++;
               row += value + "\t";
               cout << row << endl;
           }

           column = 1;
           row = "";
       }
       else
       {
           column++;
           row+=value + "\t";
       }
   }

   cout << "\nNumber of quakes greater than 6 is " << count_quake << endl;

   return 0;

} </lang>

C

<lang c>#include <stdio.h>

  1. include <string.h>
  2. include <stdlib.h>

int main() { 

   FILE *fp;
   char *line = NULL;
   size_t len = 0;
   ssize_t read;
   char *lw, *lt;
   fp = fopen("data.txt", "r");
   if (fp == NULL) {
       printf("Unable to open file\n");
       exit(1);
   }
   printf("Those earthquakes with a magnitude > 6.0 are:\n\n");
   while ((read = getline(&line, &len, fp)) != EOF) {
       if (read < 2) continue;   /* ignore blank lines */
       lw = strrchr(line, ' ');  /* look for last space */
       lt = strrchr(line, '\t'); /* look for last tab */
       if (!lw && !lt) continue; /* ignore lines with no whitespace */
       if (lt > lw) lw = lt;     /* lw points to last space or tab */
       if (atof(lw + 1) > 6.0) printf("%s", line);
   }
   fclose(fp);
   if (line) free(line);
   return 0;

}</lang>

Output:

Using the given file: 

Those earthquakes with a magnitude > 6.0 are:

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6


Cixl

<lang cixl> use: cx;

'data.txt' `r fopen lines { 

 let: (time place mag) @@s split ..;
 let: (m1 m2) $mag @. split &int map ..;
 $m1 6 >= $m2 0 > and {[$time @@s $place @@s $mag] say} if

} for </lang>

Output:
8/27/1883 Krakatoa 8.8
5/18/1980 MountStHelens 7.6

Go

<lang go>package main

import ( 

   "bufio"
   "fmt"
   "os"
   "strconv"
   "strings"

)

func main() { 

   f, err := os.Open("data.txt")
   if err != nil {
       fmt.Println("Unable to open the file")
       return
   }
   defer f.Close()
   fmt.Println("Those earthquakes with a magnitude > 6.0 are:\n")
   input := bufio.NewScanner(f)
   for input.Scan() {
       line := input.Text()
       fields := strings.Fields(line)
       mag, err := strconv.ParseFloat(fields[2], 64)
       if err != nil {
           fmt.Println("Unable to parse magnitude of an earthquake")
           return
       }
       if mag > 6.0 {
           fmt.Println(line)
       }
   }

}</lang>

Output:
Those earthquakes with a magnitude > 6.0 are:

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6

Kotlin

<lang scala>// Version 1.2.40

import java.io.File

fun main(args: Array<String>) { 

   val r = Regex("""\s+""")
   println("Those earthquakes with a magnitude > 6.0 are:\n")
   File("data.txt").forEachLine {
       if (it.split(r)[2].toDouble() > 6.0) println(it)
   }

}</lang>

Output:

Using the given file: 

Those earthquakes with a magnitude > 6.0 are:

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6

Lua

For each line, the Lua pattern "%S+$" is used to capture between the final space character and the end of the line. <lang lua>-- arg[1] is the first argument provided at the command line for line in io.lines(arg[1] or "data.txt") do -- use data.txt if arg[1] is nil 

 magnitude = line:match("%S+$")
 if tonumber(magnitude) > 6 then print(line) end

end</lang>

Perl

<lang perl>perl -n -e '/(\S+)\s*$/ and $1 > 6 and print' data.txt</lang>

Perl 6

Works with: Rakudo version 2018.03

Pass in a file name, or use default for demonstration purposes. <lang perl6>$_ = @*ARGS[0] ?? @*ARGS[0].IO !! q:to/END/; 

   8/27/1883    Krakatoa            8.8
   5/18/1980    MountStHelens       7.6
   3/13/2009    CostaRica           5.1
   END

map { .say if .words[2] > 6 }, .lines;</lang>

Python

Typed into a bash shell or similar: <lang python>python -c ' with open("data.txt") as f: 

   for ln in f:
       if float(ln.strip().split()[2]) > 6:
           print(ln.strip())'</lang>

Ring

<lang ring>

  1. Project Kernighans large earthquake problem
  2. Date 2018/06/15
  3. Author Gal Zsolt [~ CalmoSoft ~]
  4. Email <calmosoft@gmail.com>

load "stdlib.ring" nr = 0 equake = list(3) revarr = list(3) fn = "equake.txt" fp = fopen(fn,"r")

while not feof(fp) 

        nr = nr + 1 
        equake[nr] = readline(fp)

end fclose(fp) for n = 1 to len(equake) 

    revarr[n] = revstr(equake[n])

next for n = 1 to len(revarr) 

    sp = substr(revarr[n]," ")
    sptemp = substr(revarr[n],1,sp-1)
    sptemp = revstr(sptemp)
    sptemp = number(sptemp)
    if sptemp > 6
       see equake[n] + nl
    ok

next

func getFileSize(fp) 

      c_filestart = 0
      c_fileend = 2
      fseek(fp,0,c_fileend)
      nfilesize = ftell(fp)
      fseek(fp,0,c_filestart)
      return nfilesize

func revstr(cstr) 

      cStr2 = ""
      for x = len(cstr) to 1 step -1 
           cstr2 = cstr2 + cstr[x] 
      next
      return cStr2

</lang> Output: 

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens    7.6

Ruby

ruby -nae "$F[2].to_f > 6 && print" data.txt

A more interesting problem. Print only the events whose magnitude is above average.

Contents of the file: 

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6
3/13/2009    CostaRica           5.1
2000-02-02  Foo               7.7
1959-08-08   Bar             6.2
1849-09-09  Pym                9.0

The command: 

ruby -e"m=$<.to_a;f=->s{s.split[2].to_f};a=m.reduce(0){|t,s|t+f[s]}/m.size;puts m.select{|s|f[s]>a}" e.txt

Output: 

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6
2000-02-02  Foo               7.7
1849-09-09  Pym                9.0

Scala

<lang Scala>object Equakes extends App { 

 val HeavyMag = 6.0
 val regex = """^.*?((?:[0-9]{1,4}[.\-\/]){2}[0-9]{2,4})(?:\s*)([\sa-zA-Z]+)((?:0|(?:[1-9][0-9]*))(?:\.[0-9]+))?.*?$""".r

 val heavyOnes: Seq[String] = io.Source.fromFile("equake.txt").getLines().map {
   case s@regex(_, _, mag)
     if mag.toDouble > HeavyMag => s
   case _ => ""
 }.filter(_.nonEmpty).toSeq

 println(s"Events with a magnitude greater than $HeavyMag are:\n")
 heavyOnes.foreach(println(_))
 println(s"End of list of ${heavyOnes.length} events.")

}</lang>

Output:
Events with a magnitude greater than 6.0 are:

8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6


End of list of 2 events.

Tcl

Inspired by awk. <lang tcl>catch {console show} ;## show console when running from tclwish catch {wm withdraw .}

set filename "data.txt" set fh [open $filename] set NR 0 ;# number-of-record, means linenumber

while {[gets $fh line]>=0} { ;# gets returns length of line, -1 means eof 

   incr NR
   set  line2 [regexp -all -inline {\S+} $line]  ;# reduce multiple whitespace
   set  fld   [split $line2]  	;# split line into fields, at whitespace
   set  f3    [lindex $fld 2] 	;# zero-based
  #set  NF    [llength $fld]   	;# number-of-fields

   if {$f3 > 6} { puts "$line" }

} close $fh </lang>

zkl

While lexical comparsions [of numeric data] are fine for this problem, it is bad practice so I don't do it (written so text is automatically converted to float). <lang zkl>fcn equake(data,out=Console){ 

  data.pump(out,fcn(line){ 6.0line.split()[-1] },Void.Filter)

}</lang> <lang zkl>equake(Data(Void,

  1. <<<

"8/27/1883 Krakatoa 8.8\n" "5/18/1980 MountStHelens 7.6\n" "3/13/2009 CostaRica 5.1\n"

  1. <<<

));</lang> or <lang zkl>equake(File("equake.txt"));</lang> or <lang zkl>$ zkl --eval 'File.stdin.pump(Console,fcn(line){ 6.0<line.split()[-1] },Void.Filter)' < equake.txt</lang>

Output:
8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6
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