mongodb计算差值

Question

请教大家一个问题，怎么用mongodb做下面的计算，
用CameraId分组，RowTime相差小于5 ，认为两个人有伴随关系，
类似下面的数据，People a 和b ,b和c有伴随关系，a和c没有伴随
{
"RowTime":100,
"CameraId":"camera1",
"People":"a"
}
{
"RowTime":103,
"CameraId":"camera1",
"People":"b"
}
{
"RowTime":108,
"CameraId":"camera1",
"People":"c"
}