Hi Kai, Many thanks for your response. I will look at the links you sent me and I will be back to you.
Regards, Daniel T. Yehdego Computational Science Program University of Texas at El Paso, UTEP [email protected] > Subject: Re: Reducer to concatenate string values > From: [email protected] > Date: Tue, 20 Sep 2011 07:53:56 +0200 > To: [email protected] > > Hi Daniel, > > the values for a single key will be passed to reduce() in a non-predictable > order. Actually, when running the same job on the same data again, the order > is most likely different every time. > > If you want the values to be in a sorted way, you need to apply a 'secondary > sort'. The basic idea is to attach your values to the key, and then benefit > from the sorting Hadoop does on the key. > > However, you need to write some code to make that happen. Josh wrote a nice > series of articles on it, and you will find more if you google for "secondary > sort". > > http://www.cloudera.com/blog/2011/03/simple-moving-average-secondary-sort-and-mapreduce-part-1/ > http://www.cloudera.com/blog/2011/03/simple-moving-average-secondary-sort-and-mapreduce-part-2/ > http://www.cloudera.com/blog/2011/04/simple-moving-average-secondary-sort-and-mapreduce-part-3/ > > Kai > > Am 20.09.2011 um 07:43 schrieb Daniel Yehdego: > > > > > Good evening, > > I have a certain value output from a mapper and I want to concatenate the > > string outputs using a Reducer (one reducer).But the order of the > > concatenated string values is not in order. How can I use a reducer that > > receives a value from a mapper output and concatenate the strings in order. > > waiting your response and thanks in advance. > > > > Regards, > > > > Daniel T. Yehdego > > Computational Science Program > > University of Texas at El Paso, UTEP > > [email protected] > > -- > Kai Voigt > [email protected] > > > >
