从多维数组中提取和分组数据

Question

I want to print out information from a multidimensional array.

Here is my array structure:

// A two-dimensional array
$cars=array
(
    array('service' => "Windows8",'host' => Sydney1,'state' => on),
    array('service' => "unix",'host' => Newyork2,'state' => off),
    array('service' => "Windows8",'host' => Singapore3,'state' => on),
    array('service' => "unix",'host' => Tokyo4,'state' => off),
    array('service' => "Windows8",'host' => Tokyo4,'state' => on),
);

I want to arrange the data to print out the following:

Data grouped by service: desired output:

Windows8 (3): Sydney1 (on), Singapore3 (on), Tokyo4 (on) 
unix (2): Newyork2 (off), Tokyo4 (off)

Data grouped by host: desired output:

Sydney1 (1): Windows8 (on)
Newyork2 (1): unix (off)
Singapore3 (1): Windows8 (on)
Tokyo4 (2): unix (off), Windows8 (on)

Here is the code I have tried so far:

    $arr = array();

    foreach($cars as $key => $item)
    {
       $arr[$item['service_name']][$key] = $item;
    }
    echo '<pre>';    
    print_r($arr);
    echo '</pre>';

    $size = sizeof($arr);
    $i=1;
    foreach($arr as $key => $item)
    {
        echo $key;
    }

Answer 1

The trick to manipulating arrays is to arranging them into data structures that will make it easy for you to retrieve the data you need.

$cars=array (
       array('service' => "Windows8",'host' => 'Sydney1','state' => 'on'),
       array('service' => "unix",'host' => 'Newyork2','state' => 'off'),
       array('service' => "Windows8",'host' => 'Singapore3','state' => 'on'),
       array('service' => "unix",'host' => 'Tokyo4','state' => 'off'),
       array('service' => "Windows8",'host' => 'Tokyo4','state' => 'on'),
);

# initialise an array to group data by service and by location
$data = array();

foreach ($cars as $c) {
    # the key is the service name, and the value is an array of host/state pairs
    $data['by_service'][ $c['service'] ][] = array( $c['host'] , $c['state'] );

    # the key is the location name, and the value is an array of service/state pairs
    $data['by_location'][ $c['host'] ][] = array( $c['service'] , $c['state'] );
}

# create a function that we can use to print data from the pairs in the
# data structures above: it creates a string with the first array item
# followed by the second item in brackets
function print_arr ($arr) {
    return $arr[0] . " (" . $arr[1] . ")";
}

# group by service:
foreach ($data['by_service'] as $s => $host) {
    # print the service type, $s, and count the number of hosts
    echo "$s (" . count($host) . "): ";

    # print the details for the individual hosts, using print_arr for the details
    # array_map is an extremely useful function that allows you to apply a function
    # to every member of an array. It saves having to create new arrays or alter
    # the array using foreach and you can include it in an echo statement.
    echo implode(", ", array_map( "print_arr", $host ) ) . "
";
}

echo "

";

# group by location
foreach ($data['by_location'] as $l => $host) {
    # print the location and the count for the number of hosts
    echo "$l (" . count($host) . "): ";
    echo implode(", ", array_map( "print_arr", $host ) ) . "
";
}

Output:

Windows8 (3): Sydney1 (on), Singapore3 (on), Tokyo4 (on)
unix (2): Newyork2 (off), Tokyo4 (off)


Sydney1 (1): Windows8 (on)
Newyork2 (1): unix (off)
Singapore3 (1): Windows8 (on)
Tokyo4 (2): unix (off), Windows8 (on)

You might find a print_r of the $data structure helpful if you're getting lost in the code.