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
- Create a program or script invocation to find all the events with magnitude greater than 6
- Assuming an appropriate name e.g. "data.txt" for the file:
- Either: Show how your program is invoked to process a data file of that name.
- 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>#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;
}</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 $mag] say} if
} for </lang>
- Output:
8/27/1883 Krakatoa 8.8 5/18/1980 MountStHelens 7.6
Go
<lang go>package main
import (
"bufio" "fmt" "os" "strconv" "strings"
)
func main() {
f, err := os.Open("data.txt")
if err != nil {
fmt.Println("Unable to open the file")
return
}
defer f.Close()
fmt.Println("Those earthquakes with a magnitude > 6.0 are:\n")
input := bufio.NewScanner(f)
for input.Scan() {
line := input.Text()
fields := strings.Fields(line)
mag, err := strconv.ParseFloat(fields[2], 64)
if err != nil {
fmt.Println("Unable to parse magnitude of an earthquake")
return
}
if mag > 6.0 {
fmt.Println(line)
}
}
}</lang>
- Output:
Those earthquakes with a magnitude > 6.0 are: 8/27/1883 Krakatoa 8.8 5/18/1980 MountStHelens 7.6
Kotlin
<lang scala>// Version 1.2.40
import java.io.File
fun main(args: Array<String>) {
val r = Regex("""\s+""")
println("Those earthquakes with a magnitude > 6.0 are:\n")
File("data.txt").forEachLine {
if (it.split(r)[2].toDouble() > 6.0) println(it)
}
}</lang>
- Output:
Using the given file:
Those earthquakes with a magnitude > 6.0 are: 8/27/1883 Krakatoa 8.8 5/18/1980 MountStHelens 7.6
Perl
<lang perl>perl -n -e '/(\S+)\s*$/ and $1 > 6 and print' data.txt</lang>
Perl 6
Pass in a file name, or use default for demonstration purposes. <lang perl6>$_ = @*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>
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 $fh </lang>
zkl
While lexical comparsions [of numeric data] are fine for this problem, it is bad practice so I don't do it (written so text is automatically converted to float). <lang zkl>fcn equake(data,out=Console){
data.pump(out,fcn(line){ 6.0line.split()[-1] },Void.Filter)
}</lang> <lang zkl>equake(Data(Void,
- <<<
"8/27/1883 Krakatoa 8.8\n" "5/18/1980 MountStHelens 7.6\n" "3/13/2009 CostaRica 5.1\n"
- <<<
));</lang> or <lang zkl>equake(File("equake.txt"));</lang> or <lang zkl>$ 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