像获取打卡记录返回的json,如何获取到子集？

{
   "errcode":0,
   "errmsg":"ok",
   "checkindata": [{
        "userid" : "james",
        "groupname" : "打卡一组",         
        "checkin_type" : "上班打卡",      
        "exception_type" : "地点异常",   
        "checkin_time" : 1492617610,  
        "location_title" : "依澜府",    
        "location_detail" : "四川省成都市武侯区益州大道中段784号附近",  
        "wifiname" : "办公一区",         
        "notes" : "路上堵车，迟到了5分钟",
        "wifimac" : "3c:46:d8:0c:7a:70",
        "mediaids":["WWCISP_G8PYgRaOVHjXWUWFqchpBqqqUpGj0OyR9z6WTwhnMZGCPHxyviVstiv_2fTG8YOJq8L8zJT2T2OvTebANV-2MQ"],
        "sch_checkin_time" : 1492617610,
        "groupid" : 1,
        "schedule_id" : 0,
        "timeline_id" : 2
    },{
        "userid" : "paul",
        "groupname" : "打卡二组",         
        "checkin_type" : "外出打卡",      
        "exception_type" : "时间异常",   
        "checkin_time" : 1492617620,  
        "location_title" : "重庆出口加工区",    
        "location_detail" : "重庆市渝北区金渝大道101号金渝大道",  
        "wifiname" : "办公室二区",         
        "notes" : "",
        "wifimac" : "3c:46:d8:0c:7a:71",
        "mediaids":["WWCISP_G8PYgRaOVHjXWUWFqchpBqqqUpGj0OyR9z6WTwhnMZGCPHxyviVstiv_2fTG8YOJq8L8zJT2T2OvTebANV-2MQ"],
        "lat": 30547645,
        "lng": 104063236,
        "deviceid":"E5FA89F6-3926-4972-BE4F-4A7ACF4701E2",
        "sch_checkin_time" : 1492617610,
        "groupid" : 2,
        "schedule_id" : 3,
        "timeline_id" : 1
    }]
}