处理字符串拼接成想要的数组

$aa =Array(

    [R,99] => B
    [I,100] => A
    [A,101] => D
    [S,102] => C
    [E,103] => D
    [C,104] => B
    [R,105] => A
)；

$cc = array( "A" =>"1", "B" => "2", "C" => "3", "D" => "4", "E" => "5", "F" => "6", "G" => "7", );
需求：：：将aa数组里面的 r=b,然后匹配cc数组里面的值，b对应的值为2，如果aa里面有两个r那么将他们的值相加

$str ="";
foreach ($aa as $key => $v) {
	$kk = substr($key,0,1);
	$str .= substr($key,0,1)."=".$cc[$v].",";
}

　得到  str=' R=2,I=1,A=4,S=3,E=4,C=2,R=1';　

然后将str这个字符串处理成

Array
(
    [R] => 3
    [I] => 1
    [A] => 4
    [S] => 3
    [E] => 4
    [C] => 2
)
这种格式,：注意，这里拼接数组的时候，键名如果相同会被替换，需求是，如果键名相同，则键值相加
思路：
先将str以逗号打散成数组

Array
(
    [0] => R=2
    [1] => I=1
    [2] => A=4
    [3] => S=3
    [4] => E=4
    [5] => C=2
    [6] => R=1
)

循环这个数组，然后再循环里再将新数组的值，再次以=打散成新数组，

Array
(
    [0] => R
    [1] => 2
)

Array
(
    [0] => I
    [1] => 1
)

Array
(
    [0] => A
    [1] => 4
)

Array
(
    [0] => S
    [1] => 3
)

Array
(
    [0] => E
    [1] => 4
)

Array
(
    [0] => C
    [1] => 2
)

Array
(
    [0] => R
    [1] => 1
)

然后将新数组的0下标的值作为键名组成新数组，如果键名相同，键值相加，否则不用
代码：

$str = rtrim($str,",");
$arr1 = explode(',',$str);
$arr2 =[];

foreach ($arr1 as $k => $va) {
    $arr3 = explode('=',$va);
    aaa($arr3);
    if(isset($arr2[$arr3[0]])) {
        $arr2[$arr3[0]] += $arr3[1];
    }else{
        $arr2[$arr3[0]] = $arr3[1];
    }
}

function aaa($ccd){
echo "<pre>";
print_R($ccd);
echo "</pre>";

}

优化思路：不用再拼接字符串，直接判断相加

$aa = Array
(
    [R,99] => B
    [I,100] => A
    [A,101] => D
    [S,102] => C
    [E,103] => D
    [C,104] => B
    [R,105] => A
);

$cc = Array
(
    [A] => 1
    [B] => 2
    [C] => 3
    [D] => 4
    [E] => 5
    [F] => 6
    [G] => 7
);

$arr5 = [];
foreach ($aa as $key => $v) {
	$kk = substr($key,0,1);

	if(isset($arr5[$kk])){//如果键名存在，吧值相加
		$arr5[$kk] += $cc[$v];
	}else{
		$arr5[$kk] = $cc[$v];
	}
}