PHP排序功能，多维数组

Question

下面的代码起作用，并导致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'];
              });

但是，我需要通过传递一个变量作为排序参数来调用此函数，如下所示，该变量无法正确排序

$energyproportion = "'gasproportion'";

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

如何使用变量实现排序？

数组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()语法为其授予访问权限...

$energyproportion = "gasproportion";

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