PHP排序函数，多维数组

Question

下面的代码工作并产生一个从最低到最高气体比例值排序的多维数组

usort($BMEnergyArray, function($a, $b) {
return $a['gasproportion'] - $b['gasproportion'];
});

然而，我需要通过传递一个变量作为排序参数来调用这个函数，如下所示，它无法正确地对进行排序

$energyproportion = "'gasproportion'";
usort($BMEnergyArray, function($a, $b) {
return $a[$energyproportion] - $b[$energyproportion];
});

如何使用变量实现排序？

阵列中的每个项目的结构如下：

Array ( [0] => Array ( [time] => 2018-11-01 01:40:00 [gas] => 13159 [coal] => 503 [nuclear] => 5822 [wind] => 2499 [hydro] => 263 [biomass] => 3024 [solar] => 0 [gasproportion] => 52 [coalproportion] => 2 [nuclearproportion] => 23 [windproportion] => 10 [hydroproportion] => 1 [biomassproportion] => 12 [solarproportion] => 0 )

Answer 1

您可以通过function() use()语法授予它访问权限。。。

$energyproportion = "gasproportion";
usort($BMEnergyArray, function($a, $b) use ($energyproportion) {
return $a[$energyproportion] - $b[$energyproportion];
});