将数据字符串转换为csv格式

我正在组织一个名为aa的大字符串中的一些数据，并且它符合：

$print(aa)

"birthDate":"2010-01-21","tall":151,"weight":55.5,"showSize":41
,
"birthDate":"2011-05-21","tall":155,"weight":44.2,"showSize":42
,
"birthDate":"2012-11-27","tall":145,"weight":49.3,"showSize":43
,
......继续这样下去

与上面完全一样，我想把它放在csv中：birthDate，tall，weight和showSize被删除，数据只留下这样：

2010-01-21 , 151 , 55.5 , 41 "n "
2011-05-21 , 155 , 44.2 , 42 "n "
2012-11-27 , 145 , 49.3 , 43 "n "