Php (a small suspect in conditional sorting in a two-dimensional array)

Php (a small problem in sorting two-dimensional arrays by conditions) // The original Array ([1] = & gt; Array ([date] = & gt; [num] = & gt; 5) [2] = & gt; Array ([date] = & gt; 201 php (a small problem of conditional sorting in two-dimensional arrays)
// Original array
Array ([1] => Array ([date] => 2011-08-18 [num] => 5) [2] => Array ([date] => 2011-08-20 [num] => 3) [3] => Array ([date] => 2011-08-17 [num] => 10 ))

// Method 1, $ ar = Array (1 => Array ('date' => '2017-08-18 ', 'num' => 5 ), 2 => Array ('date' => '2017-08-20 ', 'num' => 3), 3 => Array ('date' => '2017-08-17 ', 'num' => 10); function mysort ($ a, $ B) {$ a = strtotime ($ a ['Date']); $ B = strtotime ($ B ['Date']); if ($ a = $ B) return 0; return ($ a <$ B )? -1: 1;} usort ($ ar, 'mysort '); print_r ($ ar ); // method 2, $ arr = array ('1' => array ('date' => '2017-08-18 ', 'num' => 5 ), '2' => array ('date' => '2017-08-20 ', 'num' => 3 ), '3' => array ('date' => '2017-08-17 ', 'num' => 10); foreach ($ arr as $ v) {$ tmp [$ v [date] = $ v;} ksort ($ tmp); print_r (array_values ($ tmp ));