Kernighans large earthquake problem

From Rosetta Code
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[edit]

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

AWK[edit]

 awk '$3 > 6' data.txt

C[edit]

#include <stdio.h>
#include <string.h>
#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;
}
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[edit]

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

Kotlin[edit]

// 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)
}
}
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

Perl[edit]

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

Perl 6[edit]

Works with: Rakudo version 2018.03

Pass in a file name, or use default for demonstration purposes.

$_ = @*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;

Python[edit]

Typed into a bash shell or similar:

python -c '
with open("data.txt") as f:
for ln in f:
if float(ln.strip().split()[2]) > 6:
print(ln.strip())'

Tcl[edit]

Inspired by awk.

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

zkl[edit]

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).

fcn equake(data,out=Console){ 
data.pump(out,fcn(line){ 6.0line.split()[-1] },Void.Filter)
}
equake(Data(Void,
#<<<
"8/27/1883 Krakatoa 8.8\n"
"5/18/1980 MountStHelens 7.6\n"
"3/13/2009 CostaRica 5.1\n"
#<<<
));

or

equake(File("equake.txt"));

or

$ zkl --eval 'File.stdin.pump(Console,fcn(line){ 6.0<line.split()[-1] },Void.Filter)' < equake.txt
Output:
8/27/1883    Krakatoa            8.8
5/18/1980    MountStHelens       7.6