使用 MAX , MIN 在 chararray 数据类型未提供预期结果。如果你想避免写作 UDF 您可以遵循以下解决方案：
我从数据开始：

1,9:00,10:00
2,8:00,11:00
3,10:00,12:00
1,11:00,13:00
1,14:00,18:00
2,12:00,18:00
3,13:00,18:00

emprec = load '/home/cloudera/pig.txt' using PigStorage(',') as (empid:int,in:chararray,out:chararray);
cleandata = foreach emprec generate $0 as ID ,(double)REPLACE($1,':','.') as in_time,(double)REPLACE($2,':','.') as out_time; --convert time to double so you can use eval functions  on it
aggdata = group cleandata by ID; 
emptime = foreach aggdata generate group ,MIN(cleandata.in_time),MAX(cleandata.out_time);
results = foreach emptime generate $0 as Emp_ID,REPLACE((chararray)($2 - $1),'\\.(?s)','\\:0') as time_diff; --convert back to time
dump results;

输出：

(1,9:00)
(2,10:00)
(3,8:00)

如果您有兴趣创建pig udf，那么下面是代码：

package Conversion;
import java.io.IOException;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.Tuple;
public class ConvertDot extends EvalFunc<String> {
@Override
public String exec(Tuple input) throws IOException {
    String newstr = new String();
    if(input == null || input.size() == 0)
        return null;
    try{
        String str = (String)input.get(0);
        if(str.contains(":"))
            newstr = str.replace(':','.');
        else if(str.contains("."))
            newstr = str.replace('.',':');
        else
            newstr = str;
    }catch (Exception e){
        throw new IOException("Caught exception ", e);
    }
    return newstr;
    }
}

$ cat ComputeTotalTime.pig
    --Calculate Min, Man and Total time
    REGISTER /home/hadoop/Desktop/Abhinav/ConvertDotColon.jar
    emprec = LOAD '/home/hadoop/Desktop/Abhinav/swaptime.txt' USING       PigStorage(',')  AS (empid:int, in:chararray, out:chararray);
    cleandata = FOREACH emprec GENERATE empid, (double)Conversion.ConvertDot(in) as in, (double)Conversion.ConvertDot(out) as out;
    aggdata = group cleandata by empid;
    emptime = foreach aggdata generate group, MIN(cleandata.in), MAX(cleandata.out);
    results = foreach emptime generate $0 as EmpId, Conversion.ConvertDot((chararray)($2 - $1)) as Time_diff;
    STORE results INTO '/home/hadoop/Desktop/Abhinav/TotalTime.txt';