为什么我不能用 foreach 循环更新数组中的数据?

我正在尝试对数组中的数据运行清理作业，特别是将纪元时间转换为 YYYY-MM-DD.

我最初尝试过这个功能:

foreach ($data as $row) {$row['eventdate'] = date('Y-m-d', $row['eventdate']);}echo '
';打印_r($数据);echo '</pre>';
但是，当我输出数据时，foreach 循环并没有更新数据.
以下 for 循环确实有效:
for ($i=0; $i
为什么第一个循环失败而第二个循环成功?他们不一样吗?
 解决方案 
当您以目前的方式使用 foreach 循环时，foreach ($data as $row){, $row 被按值"使用，而不是按引用".
尝试通过将 & 添加到 $row 来更新引用:
foreach ($data as &$row) {$row['eventdate'] = date('Y-m-d', $row['eventdate']);
或者，您可以使用键/值方法:
foreach ($data as $index => $row) {$data[$index]['eventdate'] = date('Y-m-d', $row['eventdate']);
I'm trying to run a clean up job on data in an array, specifically converting epoch time to YYYY-MM-DD.

I tried this function originally:
foreach ($data as $row) {
    $row['eventdate'] = date('Y-m-d', $row['eventdate']);
}

echo '<pre>';
print_r($data);
echo '</pre>';
However the foreach loop didn't update the data when I output it.

The following for loop did work:
for ($i=0; $i<count($data); $i++) {
    $data[$i]['eventdate'] = date('Y-m-d', $data[$i]['eventdate']);
}
Why did the first loop fail and the second work? Aren't they the same?
 解决方案 
When you're using a foreach loop in the way you currently are, foreach ($data as $row) {, $row is being used "by-value", not "by-reference".

Try updating to a reference by adding the & to the $row:
foreach ($data as &$row) {
    $row['eventdate'] = date('Y-m-d', $row['eventdate']);
Or, you can use the key/value method:
foreach ($data as $index => $row) {
    $data[$index]['eventdate'] = date('Y-m-d', $row['eventdate']);