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[{"uuid":"3fadb39c-e19b-44af-846e-29ef6766433d","url":"http://xx.com/detail/ajax.do","time":"1409","ua":"Mozilla/5.0 (Linux; U; Android 4.4.2; zh-CN; Coolpad 8297 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98241 Mobile Safari/537.36"}, {"uuid":"undefined","url":"http://xx.com/ad/ajax.do","time":"298","ua":"Mozilla/5.0 (Linux; Android 4.3; zh-CN; YUSUN L63 Build/JLS36C) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98306 Safari/534.30"}, {"uuid":"3fadb39c-e19b-44af-846e-29ef6766433d","url":"http://xx.com/ad/ajax.do","time":"1008","ua":"Mozilla/5.0 (Linux; U; Android 4.4.2; zh-CN; Coolpad 8297 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98241 Mobile Safari/537.36"}, {"uuid":"970119c8-3b2c-4217-a6c0-234500f3c050","url":"list","time":"187139","ua":"Mozilla/5.0 (Linux; U; Android 4.4.2; zh-CN; LA5-W Build/YUSUNLA5-W) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98306 Mobile Safari/537.36"}, {"uuid":"864d4099-e698-47b8-832b-a753e9c61e94","url":"list","time":"584","ua":"Mozilla/5.0 (Linux; U; Android 4.4.4; zh-CN; OKA1 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98306 Mobile Safari/537.36"}, {"uuid":"970119c8-3b2c-4217-a6c0-234500f3c050","url":"http://xx.com/ad/ajax.do","time":"689","ua":"Mozilla/5.0 (Linux; U; Android 4.4.2; zh-CN; LA5-W Build/YUSUNLA5-W) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 OPR/11.0.0.98306 Mobile Safari/537.36"},...]
现有大量log数据格式如上，其中url有http链接detail/ajax,list/ajax，字符串"list","detail","beauty"这五种情况。
现在要再这万条数据中把这五类分出来，常规写法：
for (; i < len; i++) { if(data[i][‘uuid‘] === ‘undefined‘){ undefCount++ continue; } if(data[i][‘url‘]===‘list‘){ list.push(data[i]); }else if(data[i][‘url‘]===‘detail‘){ detail.push(data[i]); }else if(data[i][‘url‘]===‘beauty‘){ beauty.push(data[i]); }else if(data[i][‘url‘].indexOf(‘list/ajax.do‘)+1){ listAjax.push(data[i]); }else if(data[i][‘url‘].indexOf(‘detail/ajax.do‘)+1){ detailAjax.push(data[i]); } }
写完之后发现11000条数据要花费1000ms的时间，感觉有点慢了。遂想到字符串的indexOf的性能非常好，于是改造一下循环：
var urlStr = ‘listdetailbeautyhttp://xx.com/list/ajax.dohttp://xx.com/detail/ajax.do‘; for (; i < len; i++) { if(data[i][‘uuid‘] === ‘undefined‘){ undefCount++ continue; } switch (urlStr.indexOf(data[i][‘url‘])){ case 0: list.push(data[i]); break; case 4: detail.push(data[i]); break; case 10: beauty.push(data[i]); break; case 16: listAjax.push(data[i]); break; case 42: detailAjax.push(data[i]); break; default : break; } }
构造一个urlStr的字符串，然后通过indexOf进行分类，同样的数据量运行居然只需要3ms，极大提升了效率。
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原文地址：http://www.cnblogs.com/childsplay/p/5057459.html
