以下是我的数组。我需要根据每个 emp_firstname 添加它的 Sum 字段。有的只来一次，有的来两次。我们如何对字段求和并使数组唯一？
Array
(
[0] => Array
(
[emp_firstname] => Alistair
[non_pm] => AMZ
[sum] => 2
)
[1] => Array
(
[emp_firstname] => Shakkeer
[non_pm] => SHK
[sum] => 3
)
[2] => Array
(
[emp_firstname] => Waqas
[non_pm] => WAS
[sum] => 12
)
[3] => Array
(
[emp_firstname] => Zain
[non_pm] => ZAI
[sum] => 9
)
[4] => Array
(
[emp_firstname] => Shakkeer
[gud_pmeditor] => SHK
[sum] => 4
)
[5] => Array
(
[emp_firstname] => Zain
[gud_pmeditor] => ZAI
[sum] => 2
)
)