PHP在多维数组中找到第二高的元素值

Question

How can i get the second highest element value in a multidimensional array. I use this function to get the highest value. But how can i find the second highest.

function get_max($array)
{
    $max = -999999999;
    $found_item = null;

    foreach ($array as $key => $value) {
        if ($value['transaction_no'] > $max) {
           $max = $value['transaction_no'];
           $found_item = $value;
        }
    }

    return $found_item;
}

For example if i call get_max($transactions) i get the array number 4 because it has the highest value: 5 in the transaction_no . But how can i get the second highest? for example when i call for get_second_max($transactions) i should get array number 3 because it has 4 in the transaction_no.

$transactions = Array
    (
        [0] => Array
            (
                [transaction_user_id] => 359691e27b23f8ef3f8e1c50315cd506
                [transaction_no] => 1
                [transaction_total_amount] => 589.00
                [transaction_date] => 1335932419
                [transaction_status] => cancelled
            )

        [1] => Array
            (
                [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
                [transaction_no] => 2
                [transaction_total_amount] => 79.00
                [transaction_date] => 1336476696
                [transaction_status] => cancelled
            )

        [2] => Array
            (
                [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
                [transaction_no] => 3
                [transaction_total_amount] => 299.00
                [transaction_date] => 1336476739
                [transaction_status] => cancelled
            )

        [3] => Array
            (
                [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
                [transaction_no] => 4
                [transaction_total_amount] => 79.00
                [transaction_date] => 1336476927
                [transaction_status] => cancelled
            )

        [4] => Array
            (
                [transaction_user_id] => 8e9050a3646c98342b9ba079fba80982
                [transaction_no] => 5
                [transaction_total_amount] => 129.00
                [transaction_date] => 1336477032
                [transaction_status] => cancelled
            )

    )

Answer 1

When a larger value than current max value is found, you know that the current max value is the 2nd largest till now. Or if there's a larger value found which is less than or equal to current max value while larger than the current second largest, update the current second largest accordingly.

Updated Code:

function get_max($array) {
    $max = -999999999;
    $max_item = null;
    $second_max_item = null;
    foreach($array as $key=>$value)
    {
        if($value['transaction_no'] >= $max)
        {
            $max = $value['transaction_no'];
            $second_max_item = $max_item;
            $max_item = $value;

        } else if($value['transaction_no'] > $second_max_item['transaction_no']) {

            $second_max_item = $value;

        }
     }

    return $second_max_item;
}

Answer 2

<?php
function get_max($array) {

    $all = array();
    foreach($array as $key=>$value){
        $all[] = $value['transaction_no'];
    }

    rsort($all);
    return $all[1];
}

To return the array and not only the value:

function get_max($array) {

    $all = array();
    foreach($array as $key=>$value){
        /* creating array where the key is transaction_no and
           the value is the array containing this transaction_no */
        $all[$value['transaction_no']] = $value;
    }

    /* now sort the array by the key (transaction_no) */
    krsort($all);

    /* get the second array and return it (see the link below) */
    return array_slice($all, 1, 1)[0];
}

PHP: Get n-th item of an associative array

Answer 3

For testing purposes your given array

$transactions = array(
    array(
        'transaction_user_id'       => '359691e27b23f8ef3f8e1c50315cd506',
        'transaction_no'            => 1,
        'transaction_total_amount'  => 589.00,
        'transaction_date'          => 1335932419,
        'transaction_status'        => 'cancelled',
    ),
    array(
        'transaction_user_id'       => '9def02e6337b888d6dbe5617a172c18d',
        'transaction_no'            => 2,
        'transaction_total_amount'  => 79.00,
        'transaction_date'          => 1336476696,
        'transaction_status'        => 'cancelled',
    ),
    array(
        'transaction_user_id'       => '9def02e6337b888d6dbe5617a172c18d',
        'transaction_no'            => 3,
        'transaction_total_amount'  => 299.00,
        'transaction_date'          => 1336476739,
        'transaction_status'        => 'cancelled',
    ),
    array(
        'transaction_user_id'       => '9def02e6337b888d6dbe5617a172c18d',
        'transaction_no'            => 4,
        'transaction_total_amount'  => 79.00,
        'transaction_date'          => 1336476927,
        'transaction_status'        => 'cancelled',
    ),
    array(
        'transaction_user_id'       => '8e9050a3646c98342b9ba079fba80982',
        'transaction_no'            => 5,
        'transaction_total_amount'  => 129.00,
        'transaction_date'          => 1336477032,
        'transaction_status'        => 'cancelled',
    ),
);

A simple function to get the n-th ancestor of the maximum transaction number.

It retrieves your array with the transactions and the index of the ancestor you want. Internally it checks wether your array is large enough to get the defined ancestor, sorts the given array by the transaction number and returns the n-th (ancestor-th) element.

function getTransactionMaxAncestor($transactions, $ancestor = 0)
{
    if ($ancestor > count($transactions)) {
        throw new Exception('Not enough transactions available');
    }   

    usort($transactions, function ($a, $b) {
        $ta = $a['transaction_no'];
        $tb = $b['transaction_no'];

        if ($a == $b) {
            return 0;
        }

        return $a > $b ? -1 : 1;
    });

    return $transactions[$ancestor];
}

The relevant call to get the second highest element

$secondHighest = getTransactionMaxAncestor($transactions, 1);