我的阵列会发生什么？ 物品消失了

what happens with my result array here? i expected the size of the result array to be equal to the input array, but its missing 3 entries.. where did they go? they didn't go to $ret , as they were supposed to..

code:

<?php
init();
$list_xy = array(
    0 => array(
        'id' => '308',
        'x' => '37',
        'y' => '63'
    ),
    1 => array(
        'id' => '963',
        'x' => '38',
        'y' => '134'
    ),
    2 => array(
        'id' => '385',
        'x' => '39',
        'y' => '132'
    ),
    3 => array(
        'id' => '1231',
        'x' => '50',
        'y' => '199'
    ),
    4 => array(
        'id' => '788',
        'x' => '51',
        'y' => '59'
    ),
    5 => array(
        'id' => '1151',
        'x' => '53',
        'y' => '61'
    ),
    6 => array(
        'id' => '671',
        'x' => '55',
        'y' => '60'
    ),
    7 => array(
        'id' => '1487',
        'x' => '55',
        'y' => '55'
    )
);
$sorted_list_xy = sort_by_xy_distance($list_xy);
$sorted_list_xy_size = count($sorted_list_xy, COUNT_NORMAL);
$list_xy_size = count($list_xy, COUNT_NORMAL);
var_dump($sorted_list_xy_size == $list_xy_size ? "looks right" : "something is wrong", $sorted_list_xy_size, $list_xy_size);
die("died");


function sort_by_xy_distance($input_list)
{
    $ret = array();
    $a = $input_list[0];
    array_push($ret, $input_list[0]);
    $input_list[0] = null;
    $i = 1;
    for ($i = 1; $i < count($input_list); ++$i) {
        if ($input_list[$i] == null) {
            echo 'already added to list..';
            continue;
        }
        $ii = 1;
        $tmpdistance = 0;
        $nearest = array(
            'index' => -1,
            'distance' => PHP_INT_MAX
        );
        for ($ii = 1; $ii < count($input_list); ++$ii) {
            if ($input_list[$ii] == null || $ii == $i) {
                //echo 'already added to list..';
                continue;
            }
            $tmpdistance = abs($input_list[$ii]['x'] - $a['x']) + abs($input_list[$ii]['y'] - $a['y']);
            if ($tmpdistance < $nearest['distance']) {
                $nearest['index'] = $ii;
                $nearest['distance'] = $tmpdistance;
            }
        }
        assert($nearest['index'] != -1);
        array_push($ret, $input_list[$nearest['index']]);
        $a = $input_list[$nearest['index']];
        $input_list[$nearest['index']] = null;
    }
    return $ret;
}





function init()
{
    error_reporting(E_ALL);
    set_error_handler("exception_error_handler");
}
function exception_error_handler($errno, $errstr, $errfile, $errline)
{
    if (!(error_reporting() & $errno)) {
        // This error code is not included in error_reporting
        return;
    }
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}

output:

already added to list..already added to list..already added to list..string(18) "something is wrong" int(5) int(8) died

expected output: (something similar to)

already added to list..already added to list..already added to list..string(11) "looks right" int(8) int(8) died

what i expected the list to turn in to: a list where the difference to the next's [x][y] is as little as possible, which would be:

array(8) {
  [0]=>
  array(3) {
    ["id"]=>
    string(3) "308"
    ["x"]=>
    string(2) "37"
    ["y"]=>
    string(2) "63"
  }
  [1]=>
  array(3) {
    ["id"]=>
    string(3) "788"
    ["x"]=>
    string(2) "51"
    ["y"]=>
    string(2) "59"
  }
  [2]=>
  array(3) {
    ["id"]=>
    string(4) "1151"
    ["x"]=>
    string(2) "53"
    ["y"]=>
    string(2) "61"
  }
  [3]=>
  array(3) {
    ["id"]=>
    string(3) "671"
    ["x"]=>
    string(2) "55"
    ["y"]=>
    string(2) "60"
  }
  [4]=>
  array(3) {
    ["id"]=>
    string(4) "1487"
    ["x"]=>
    string(2) "55"
    ["y"]=>
    string(2) "55"
  }
  [5]=>
  array(3) {
    ["id"]=>
    string(3) "385"
    ["x"]=>
    string(2) "39"
    ["y"]=>
    string(3) "132"
  }
  [6]=>
  array(3) {
    ["id"]=>
    string(3) "963"
    ["x"]=>
    string(2) "38"
    ["y"]=>
    string(3) "134"
  }
  [7]=>
  array(3) {
    ["id"]=>
    string(4) "1231"
    ["x"]=>
    string(2) "50"
    ["y"]=>
    string(3) "199"
  }
}

I suck at making graphical illustrations, but ill give it a go. This is my map: map http://imagizer.imageshack.us/a/img633/3521/E0HGRe.png

i need to visit all the black dots. This is my current path:

this path is not very optimal.. here is the path i want:

and that's what the sort function is trying to find, the shortest path to visit all the black dots.

Distance calculation you should use Pythagoras' theorem (or just hypot, like @prodigitalson mentioned). For geo coordinates you could use this: http://www.movable-type.co.uk/scripts/latlong.html

Let's fix your code. Every step of your first loop should take one value from input value and place it into result. But it has continue inside, therefor some steps of first loop do not do their job. Try to remove first continue.

$list_xy = array(
    0 => array(
        'id' => '308',
        'x' => '37',
        'y' => '63'
    ),
    1 => array(
        'id' => '963',
        'x' => '38',
        'y' => '134'
    ),
    2 => array(
        'id' => '385',
        'x' => '39',
        'y' => '132'
    ),
    3 => array(
        'id' => '1231',
        'x' => '50',
        'y' => '199'
    ),
    4 => array(
        'id' => '788',
        'x' => '51',
        'y' => '59'
    ),
    5 => array(
        'id' => '1151',
        'x' => '53',
        'y' => '61'
    ),
    6 => array(
        'id' => '671',
        'x' => '55',
        'y' => '60'
    ),
    7 => array(
        'id' => '1487',
        'x' => '55',
        'y' => '55'
    )
);
$sorted_list_xy = sort_by_xy_distance($list_xy);
$sorted_list_xy_size = count($sorted_list_xy, COUNT_NORMAL);
$list_xy_size = count($list_xy, COUNT_NORMAL);
var_dump($sorted_list_xy_size == $list_xy_size ? "looks right" : "something is wrong", $sorted_list_xy_size, $list_xy_size);
die("died");

function sort_by_xy_distance($input_list)
{
    $ret = array();
    $a = $input_list[0];
    array_push($ret, $input_list[0]);
    $input_list[0] = null;
    $i = 1;
    for ($i = 1; $i < count($input_list); ++$i) {
//                                                         up here
//        if ($input_list[$i] == null) {
//            echo 'already added to list..';
//            continue;
//        }
        $ii = 1;
        $tmpdistance = 0;
        $nearest = array(
            'index' => -1,
            'distance' => PHP_INT_MAX
        );
        for ($ii = 1; $ii < count($input_list); ++$ii) {
            if ($input_list[$ii] == null || $ii == $i) {
                //echo 'already added to list..';
                continue;
            }
            $tmpdistance = abs($input_list[$ii]['x'] - $a['x']) + abs($input_list[$ii]['y'] - $a['y']);
            if ($tmpdistance < $nearest['distance']) {
                $nearest['index'] = $ii;
                $nearest['distance'] = $tmpdistance;
            }
        }
        assert($nearest['index'] != -1);
        array_push($ret, $input_list[$nearest['index']]);
        $a = $input_list[$nearest['index']];
        $input_list[$nearest['index']] = null;
    }
    return $ret;
}