Brian:
Thanks for your response.
I have 8 total keys and values. The code I show below is part of the whole
thing, just to illustrate my problem.
Im trying to call each key with an if statement (as in the piece I showed
before). Each of my 8 keys have their respective if statement.
However, it seems that my if statement is not going through. I even put
the output.collect(...) inside the if statement, and accordingly, no
output was shown. I already tested my mapper, and it seems to work fine.
I believe that I am having difficulty at this point:
if (key.equals("sex")) {...}
The key in this case is "sex" (or gender) and the possible values are 0
(for male) and 1 (for female). Is this not the right way to separate out
my keys?
-Reza
> Hey Reza,
>
> From reading your code, you are calling this for the key "sex":
>
> output.collect("The total population is: ", (actual population))
>
> and, for every other key:
>
> output.collect("The total population is: ", 0)
>
> You probably only want to call the output collector in the first case,
> not every time.
>
> Brian
>
>
> On Apr 18, 2009, at 12:21 PM, Reza wrote:
>
>> Hello all:
>>
>> I am new to Hadoop and Map Reduce. I am writing a program to analyze
>> some
>> census data.
>>
>> I have a general question with MapReduce:
>>
>> In the Reducer, how can I separate keys to do separate calculations
>> based
>> on the key? In my case, I am trying to use if statements to separate
>> the
>> keys out, but for some reason, it is not doing so.
>>
>> Here is a segment of my code. My mapper seems to work, I think it is
>> my
>> Reducer that is messing up:
>>
>> public static class MapClass extends MapReduceBase implements
>> Mapper<LongWritable, Text, Text, IntWritable> {
>>
>> // private final static IntWritable one = new IntWritable(1);
>> Text sex = new Text("sex");
>> public void map(LongWritable key, Text value,
>> OutputCollector<Text, IntWritable> output,
>> Reporter reporter) throws IOException {
>> String line = value.toString();
>> StringTokenizer itr = new StringTokenizer(line,",");
>>
>> :
>> :
>> word.set(itr.nextToken());
>> IntWritable sexVal = new
>> IntWritable(Integer.parseInt(word.toString())); //map gender
>> output.collect(sex, sexVal);
>>
>> }//end map()method
>> }//end class MapClass
>>
>>
>> public static class Reduce extends MapReduceBase
>> implements Reducer<Text, IntWritable, Text, IntWritable> {
>>
>>
>> public void reduce(Text key, Iterator<IntWritable> values,
>> OutputCollector<Text, IntWritable> output,
>> Reporter reporter) throws IOException {
>>
>> int totalPop = 0; //count: total population
>> int numMales = 0; //count: males
>> int numFemales = 0; //count: females
>> Text popOut = new Text("The total population is:
>> ");
>> if (key.equals("sex")) {
>> while (values.hasNext()) {
>> if (values.next().get() == 0)
>> numMales++; //number
>> of males
>> else
>> numFemales++; //number
>> of
>> females
>> }//end while
>> totalPop = numMales + numFemales; //count of population
>> }//end if
>> output.collect(popOut, new IntWritable(totalPop));
>>
>> }//end reduce method
>> }//end class Reduce
>>
>> key is of type Text, I also used: if (key.toString() == "sex) {....
>> but that wasnt working either.
>>
>> There are of course other keys and values, but I would think to
>> gather all
>> the keys "sex" would be done with the way I show it above. However,
>> My
>> output reads as 0. I tried changing the numMales value to see if
>> the if
>> statement is executed, but it is not. Am I doing something wrong?
>>
>
>
