Hi, Husain,
1. You can use a boolean control in your code.
boolean hasAlreadyOned = false;
int iCount = 0;
String sValue;
while (values.hasNext()) {
sValue = values.next().toString();
iCount++;
if (sValue.equals("1"))
hasAlreadyOned = true;
if (!hasAlreadyOned)
sValues += "\t" + sValue;
}
...
2. You're actually controlling for 3 elements, not 2. You should use if
(iCount == 1)
2009/4/1 Farhan Husain <[email protected]>
> Hello All,
>
> I am facing some problems with a reduce method I have written which I
> cannot
> understand. Here is the method:
>
> @Override
> public void reduce(Text key, Iterator<Text> values,
> OutputCollector<Text, Text> output, Reporter reporter)
> throws IOException {
> String sValues = "";
> int iCount = 0;
> String sValue;
> while (values.hasNext()) {
> sValue = values.next().toString();
> iCount++;
> sValues += "\t" + sValue;
>
> }
> sValues += "\t" + iCount;
> //if (iCount == 2)
> output.collect(key, new Text(sValues));
> }
>
> The output of the code is like the following:
>
> D0U0:GraduateStudent0 lehigh:GraduateStudent 1 1 1
> D0U0:GraduateStudent1 lehigh:GraduateStudent 1 1 1
> D0U0:GraduateStudent10 lehigh:GraduateStudent 1 1 1
> D0U0:GraduateStudent100 lehigh:GraduateStudent 1 1
> 1
> D0U0:GraduateStudent101 lehigh:GraduateStudent 1
> D0U0:GraduateCourse0 1 2 1
> D0U0:GraduateStudent102 lehigh:GraduateStudent 1 1
> 1
> D0U0:GraduateStudent103 lehigh:GraduateStudent 1 1
> 1
> D0U0:GraduateStudent104 lehigh:GraduateStudent 1 1
> 1
> D0U0:GraduateStudent105 lehigh:GraduateStudent 1 1
> 1
>
> The problem is there cannot be so many 1's in the output value. The output
> which I expect should be like this:
>
> D0U0:GraduateStudent0 lehigh:GraduateStudent 1
> D0U0:GraduateStudent1 lehigh:GraduateStudent 1
> D0U0:GraduateStudent10 lehigh:GraduateStudent 1
> D0U0:GraduateStudent100 lehigh:GraduateStudent 1
> D0U0:GraduateStudent101 lehigh:GraduateStudent
> D0U0:GraduateCourse0 2
> D0U0:GraduateStudent102 lehigh:GraduateStudent 1
> D0U0:GraduateStudent103 lehigh:GraduateStudent 1
> D0U0:GraduateStudent104 lehigh:GraduateStudent 1
> D0U0:GraduateStudent105 lehigh:GraduateStudent 1
>
> If I do not append the iCount variable to sValues string, I get the
> following output:
>
> D0U0:GraduateStudent0 lehigh:GraduateStudent
> D0U0:GraduateStudent1 lehigh:GraduateStudent
> D0U0:GraduateStudent10 lehigh:GraduateStudent
> D0U0:GraduateStudent100 lehigh:GraduateStudent
> D0U0:GraduateStudent101 lehigh:GraduateStudent
> D0U0:GraduateCourse0
> D0U0:GraduateStudent102 lehigh:GraduateStudent
> D0U0:GraduateStudent103 lehigh:GraduateStudent
> D0U0:GraduateStudent104 lehigh:GraduateStudent
> D0U0:GraduateStudent105 lehigh:GraduateStudent
>
> This confirms that there is no 1's after each of those values (which I
> already know from the intput data). I do not know why the output is
> distorted like that when I append the iCount to sValues (like the given
> code). Can anyone help in this regard?
>
> Now comes the second problem which is equally perplexing. Actually, the
> reduce method which I want to run is like the following:
>
> @Override
> public void reduce(Text key, Iterator<Text> values,
> OutputCollector<Text, Text> output, Reporter reporter)
> throws IOException {
> String sValues = "";
> int iCount = 0;
> String sValue;
> while (values.hasNext()) {
> sValue = values.next().toString();
> iCount++;
> sValues += "\t" + sValue;
>
> }
> sValues += "\t" + iCount;
> if (iCount == 2)
> output.collect(key, new Text(sValues));
> }
>
> I want to output only if "values" contained only two elements. By looking
> at
> the output above you can see that there is at least one such key values
> pair
> where values have exactly two elements. But when I run the code I get an
> empty output file. Can anyone solve this?
>
> I have tried many versions of the code (e.g. using StringBuffer instead of
> String, using flags instead of integer count) but nothing works. Are these
> problems due to bugs in Hadoop? Please let me know any kind of solution you
> can think of.
>
> Thanks,
>
> --
> Mohammad Farhan Husain
> Research Assistant
> Department of Computer Science
> Erik Jonsson School of Engineering and Computer Science
> University of Texas at Dallas
>
--
M. Raşit ÖZDAŞ
