PHP：在关联数组中累积值

Question

我想根据键的一部分在关联数组中累积值。

我已经测试了这个在索引数组中工作正常的 foreach 循环：

$b = array();

foreach ($a as $key => $value) {
  if ($key > 0) {
    $b[$key] = $b[$key - 1] + $value;
  }
}

我无法让它在关联数组中工作，但是...

$a（摘录）

Array ( 
    [2014-04-22|Paul] => 0 
    [2014-04-28|Paul] => 2 
    [2014-05-13|Paul] => 0
    [2014-06-03|Paul] => 1 
    [2014-06-12|Paul] => 0 
    [2014-08-11|Paul] => 1 
    [2014-08-28|Paul] => 3 
    [2012-05-09|John] => 1 
    [2012-08-29|John] => 2 
    [2012-09-05|John] => 0 
    [2012-09-13|John] => 1 
)

$b（想要的结果）

Array ( 
    [2014-04-22|Paul] => 0 
    [2014-04-28|Paul] => 2 
    [2014-05-13|Paul] => 2 
    [2014-06-03|Paul] => 3 
    [2014-06-12|Paul] => 3 
    [2014-08-11|Paul] => 4 
    [2014-08-28|Paul] => 7 
    [2012-05-09|John] => 1 
    [2012-08-29|John] => 3 
    [2012-09-05|John] => 3 
    [2012-09-13|John] => 4 
)

在期望的结果中，每个值都是 'Paul' 和 'John'（以及更多）累积到前一个值。

Answer 1

您可以通过跟踪键的名称部分来做到这一点，并在获得新名称时重置总数：

$b = array();
$lastname = '';
foreach ($a as $key => $value) {
    list($d, $n) = explode('|', $key);
    if ($n == $lastname) {
        $total += $value;
    }
    else {
        $total = $value;
    }
    $b[$key] = $total;
    $lastname = $n;
}
print_r($b);

输出：

Array ( 
    [2014-04-22|Paul] => 0 
    [2014-04-28|Paul] => 2 
    [2014-05-13|Paul] => 2 
    [2014-06-03|Paul] => 3 
    [2014-06-12|Paul] => 3 
    [2014-08-11|Paul] => 4 
    [2014-08-28|Paul] => 7 
    [2012-05-09|John] => 1 
    [2012-08-29|John] => 3 
    [2012-09-05|John] => 3 
    [2012-09-13|John] => 4 
)

Demo on 3v4l.org

Answer 2

通过使用array_walk，检查当前名称是否与下一个名称相同，因为我正在通过下一个重置值。

$result = [];
$tempKey = '';
$arr = array_walk($arr, function($item, $key) use(&$result, &$tempKey, &$total){
    list($date, $name) = explode("|", $key); // explode key
    if(empty($tempKey) || $tempKey != $name){ // if empty or if conflict
        $tempKey = $name; // tempKey for reference
        $total = $item; // total reset to current value
    }else{
        $total += $item; // adding for same name
    }
    $result[$key] = $total; // putting calculated value
});

print_r($result);

输出

Array
(
    [2014-04-22|Paul] => 0
    [2014-04-28|Paul] => 2
    [2014-05-13|Paul] => 2
    [2014-06-03|Paul] => 3
    [2014-06-12|Paul] => 3
    [2014-08-11|Paul] => 4
    [2014-08-28|Paul] => 7
    [2012-05-09|John] => 1
    [2012-08-29|John] => 3
    [2012-09-05|John] => 3
    [2012-09-13|John] => 4
)

Demo.