pig强制转换（字符到整数）：首位0怎么处理，‘01’到1的转化，

pig支持的类型转换（cast）Pig Latin supports casts as shown in this table.

from / to	bag	tuple	map	int	long	float	double	chararray	bytearray	boolean
bag	error	error	error	error	error	error	error	error	error
tuple	error	error	error	error	error	error	error	error	error
map	error	error	error	error	error	error	error	error	error
int	error	error	error	yes	yes	yes	yes	error	error
long	error	error	error	yes	yes	yes	yes	error	error
float	error	error	error	yes	yes	yes	yes	error	error
double	error	error	error	yes	yes	yes	yes	error	error
chararray	error	error	error	yes	yes	yes	yes	error	yes
bytearray	yes	yes	yes	yes	yes	yes	yes	yes	yes
boolean	error	error	error	error	error	error	error	yes	error

表中，将字符类型转化做int是可以的。那么001 转化为int型后是1么？测试如下数据文件test_file.txt内容为：1011,0120111,1000011,0100001,0101010,001读入test_file.txt，将第一列的chararray类型数据，提取前三个字段，强制转换为int类型。而第二列直接按int类型读入，看看首位0怎么处理pig 代码：%default testFile /user/wizad/test/lmj/test_file.txttest_data = LOAD '$testFile' USING PigStorage(',')AS(str1:chararray,number:int);dump test_data;my_result = foreach test_data generate (int)SUBSTRING(str1,0,3);dump my_result;describe my_result;--myts = sample g_log 0.0001;--myts = limit g_log 10;--dump myts;--STORE myts INTO '/user/wizad/tmp/my' USING PigStorage(',');运行结果dump test_data：(1011,12)(0111,100)(0011,10)(0001,10)(1010,1)dump my_result：(101)(11)(1)(0)(101)可以看出首位0处理没有任何问题。

顺便一提：

debug或检查数据时,能用store，不用dump。要用dump就只用dump。我dump前，都先limit 10，只dump 10条数据

因为，dump会让某些multi-query execution失效。看起来像降低运行数据。举例子：两个脚本一个执行 A > B >DUMP而另一个执行A > B > C > STORE第一个脚本：A = LOAD 'input'AS (x, y, z);B = FILTER A BY x> 5;DUMP B;C = FOREACH BGENERATE y, z;STORE C INTO'output';store脚本：生成output1和output2两个文件，执行A > B > C > STOREA = LOAD 'input'AS (x, y, z);B = FILTER A BY x> 5;STORE B INTO'output1';C = FOREACH BGENERATE y, z;STORE C INTO'output2';        

我工作中，需要比较两个日志的ip，time，os，来识别是否是相同用户。而time需要判定5分钟内相同用户。所以我做了一个小处理，将是时间从分钟切分：time_extract = foreach cookie_data generate cookie_id,ip,SUBSTRING(time,0,13) as time,SUBSTRING(time,14,16) as minute1,os_id,os_version;log_data = foreach click_log generate log_type,guid,ip,SUBSTRING(create_time,0,13) as time,SUBSTRING(create_time,14,16) as minute2,os_id,os_version;然后，将两个relation按 time进行join，就是比较到小时的：join_data = join time_extract by (ip,time,os_id), log_data by (ip,time,os_id);在相同小时的记录中，找5分钟内的：minute_compare = foreach join_data generate log_type,cookie_id,guid,(int)minute1,(int)minute2,time_extract::os_version,log_data::os_version;same_users = filter minute_compare by (ABS(minute1-minute2) <= 5);绝对值小于5的。完成代码如下:SET job.name 'mapping_from_mobile_to_pc';SET job.priority HIGH;REGISTER piggybank.jar;DEFINE SequenceFileLoader org.apache.pig.piggybank.storage.SequenceFileLoader();%default cleanedLog /user/wizad/data/wizad/cleaned/2014-11-{0[3-9],1[0-8]}/*/part*%default cookieLog /user/wizad/tmp/ip_cookie.txt%default output_path1 /user/wizad/tmp/mapping_cookie%default output_path2 /user/wizad/tmp/edition_comparecookie_data = LOAD '$cookieLog' USING PigStorage(',')AS(cookie_id:chararray,ip:chararray,time:chararray,os_id:chararray,os_version:chararray);--test = limit cookie_data 100;--dump test;time_extract = foreach cookie_data generate cookie_id,ip,SUBSTRING(time,0,13) as time,SUBSTRING(time,14,16) as minute1,os_id,os_version;describe time_extract;origin_cleaned_data = LOAD '$cleanedLog' USING SequenceFileLoaderAS (ad_network_id:chararray,wizad_ad_id:chararray,guid:chararray,id:chararray,create_time:chararray,action_time:chararray,log_type:chararray,ad_id:chararray,positioning_method:chararray,location_accuracy:chararray,lat:chararray,lon:chararray,cell_id:chararray,lac:chararray,mcc:chararray,mnc:chararray,ip:chararray,connection_type:chararray,imei:chararray,android_id:chararray,android_advertising_id:chararray,udid:chararray,openudid:chararray,idfa:chararray,mac_address:chararray,uid:chararray,density:chararray,screen_height:chararray,screen_width:chararray,user_agent:chararray,app_id:chararray,app_category_id:chararray,device_model_id:chararray,carrier_id:chararray,os_id:chararray,device_type:chararray,os_version:chararray,country_region_id:chararray,province_region_id:chararray,city_region_id:chararray,ip_lat:chararray,ip_lon:chararray,quadkey:chararray);click_log = filter origin_cleaned_data by log_type=='2';log_data = foreach click_log generate log_type,guid,ip,SUBSTRING(create_time,0,13) as time,SUBSTRING(create_time,14,16) as minute2,os_id,os_version,device_type;--join_data = join time_extract by ip, log_data by ip;--join_data = join time_extract by (ip,time), log_data by (ip,time);join_data = join time_extract by (ip,time,os_id), log_data by (ip,time,os_id);minute_compare = foreach join_data generate log_type,cookie_id,guid,(int)minute1,(int)minute2,time_extract::os_version,log_data::os_version;same_users = filter minute_compare by (ABS(minute1-minute2) <= 5);--dump same_users;describe same_users;mapping_cookie_id = foreach same_users generate cookie_id,guid;uniq_cookie_guid = distinct mapping_cookie_id;store uniq_cookie_guid INTO '$output_path1' USING PigStorage(',');os_edition = foreach same_users generate cookie_id,guid,SUBSTRING(time_extract::os_version,0,2) as os_ut,SUBSTRING(log_data::os_version,0,2) as os_mdm;same_os_edition = filter os_edition by (os_ut == os_mdm) or (os_ut == 'x')or (os_mdm == 'x');dump same_os_edition;cookie_guid_with_edition = foreach same_os_edition generate cookie_id,guid;uniq_c_g_editions = distinct cookie_guid_with_edition;store uniq_c_g_editions INTO '$output_path2' USING PigStorage(',');