Sort by distance

pglinx has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to sort this by distance (km)... All works but I just can't seem to get this to happen

open(FILE, "herbalarea.pl") || die "I can't open that because: $!\n";
     while(<FILE>) {
   chop;          @all = split(/\n/);

   foreach $line (@all) {
   local($hStoreID, $hStoreLatitude, $hStoreLongitude) = split(/    /,
+ $line);

$lat2 = $hStoreLatitude;
$lon2 = $hStoreLongitude;
$lat1 = $lat1a;
$lon1 = $lon1a;


       # Notice the 90 - latitude: phi zero is at the North Pole.
       @L = (deg2rad($lat1), deg2rad(90 - $lon1));
       @T = (deg2rad($lat2), deg2rad(90 - $lon2));
       $km = great_circle_distance(@L, @T, 6378);


#-------HERE IS THE PROBLEM---------#
@km=sort {$a <=> $b} (@zip_dist);
$km = (@zip_dist);
#-----------------------------------#

if ($km < $distance)

{
       $match = 1;
$count ++;

   $area = "$hStoreName <BR> $hStoreAdd <br>  $hStoreCity, $hStoreProv
+ $hStorePC\n";
       
$rounded = sprintf("%.1f", $km);
print "
$area $km
\n";
}
[download]

Comment on Sort by distance Download Code

Replies are listed 'Best First'.
Re: Sort by distance by ikegami (Patriarch) on May 27, 2009 at 13:52 UTC
Use `use strict; use warnings;`!!! `@zip_dist` is never assigned anything. `$km = (@zip_dist);` surely doesn't do what you want it to do. An array in scalar context returned the number of elements in the array. `$count++;` is rather useless outside of a loop.	[reply] [d/l] [select]
Re: Sort by distance by jettero (Monsignor) on May 27, 2009 at 13:53 UTC
(copy ikegami) and: I imagine you want my not local. You rarely, if ever, want local. You also seem to be missing a closing brace. I was trying to reformulate this as a Schwartzian transform, but I'm confused about what it is that you're sorting. I'd expect something like this to work, but it wont if you're comparing the distance between $a and $b -- what would the usefulness of that be? `my @sorted_points = map { $_->[0] } sort { $a->[1] <=> $b->[1] } map {[$_, dist($_, $reference_point)]} @points; # points is an AoA structure` [download] -Paul	[reply] [d/l]
Re: Sort by distance by Anonymous Monk on May 27, 2009 at 13:57 UTC
Here is what you do, insert this `use Data::Dumper; print Dumper(\@zip_dist); #-------HERE IS THE PROBLEM---------#` [download] Then, show us the output :) How (Not) To Ask A Question	[reply] [d/l]
Re: Sort by distance by DStaal (Chaplain) on May 27, 2009 at 13:56 UTC
Two questions: Where, and how, do you define `@zip_dist`? It's hard to figure out what the problem with a sort is if we can't see the data that's being sorted. And number 2: What are you trying to do in line #22? Whatever it is, something should probably have a different name. (You've got `@km` and `$km`, and I think you are trying to use them as separate variables. Which can be done, but it's going to confuse you, your maintainer, or perl. Or all three.)	[reply] [d/l] [select]
Re^2: Sort by distance by pglinx (Acolyte) on May 27, 2009 at 14:23 UTC
The section shown as the problem was nothing more then an attempt at sorting but causes the entire database to output with km equaling 0 I probably should have asked the question leaving that part out. I eliminated thing that have to do with count and other funtions to make it more brief and example.	[reply]
Re^3: Sort by distance by DStaal (Chaplain) on May 27, 2009 at 14:35 UTC
Well, you eliminated too much: The example above doesn't have enough information to answer your question.	[reply]
Re^4: Sort by distance by pglinx (Acolyte) on May 27, 2009 at 14:53 UTC
Re^5: Sort by distance by DStaal (Chaplain) on May 27, 2009 at 16:21 UTC
Re^5: Sort by distance by Marshall (Canon) on May 28, 2009 at 00:14 UTC
Re: Sort by distance by hda (Chaplain) on May 27, 2009 at 16:11 UTC
Hi, it might be a little of an overkill for your needs, but consider using PostGIS for your most complicated geographical vector analyses. Having your data points in a PostgreSQL database and accessing it with DBI is a great idea. I use it almost on a daily basis.	[reply]