MapReduce

问题 I have some counters I created at my Mapper class: (example written using the appengine-mapreduce Java library v.0.5) @Override public void map(Entity entity) { getContext().incrementCounter("analyzed"); if (isSpecial(entity)){ getContext().incrementCounter("special"); } } (The method isSpecial just returns true or false depending on the state of the entity, not relevant to the question) I want to access those counters when I finish processing the whole stuff, at the finish method of the

问题 I have some counters I created at my Mapper class: (example written using the appengine-mapreduce Java library v.0.5) @Override public void map(Entity entity) { getContext().incrementCounter("analyzed"); if (isSpecial(entity)){ getContext().incrementCounter("special"); } } (The method isSpecial just returns true or false depending on the state of the entity, not relevant to the question) I want to access those counters when I finish processing the whole stuff, at the finish method of the

问题 I have a static object in my map reduce job class that I want to initialize once (in the main method), then call a function on it in every mapping. So I have this object, MyObject that I declare as a variable: static MyObject obj; And in my main function, before I start the job I call: obj = new MyObject(); obj.init(); And then in my map function I want to call: obj.execute(); But for some reason I get a null pointer exception when I try this (it says obj is null). If I initialize it in my

问题 private static String[] testFiles = new String[] {"img01.JPG","img02.JPG","img03.JPG","img04.JPG","img06.JPG","img07.JPG","img05.JPG"}; // private static String testFilespath = "/home/student/Desktop/images"; private static String testFilespath ="hdfs://localhost:54310/user/root/images"; //private static String indexpath = "/home/student/Desktop/indexDemo"; private static String testExtensive="/home/student/Desktop/images"; public static class MapClass extends MapReduceBase implements Mapper

问题 I was wondering if there's a simple way to combine the functions of rapply( , how = "replace") and mapply() , in order to use mapply() on nested lists recursively. For instance, I have two nested lists: A = list(list(c(1,2,3), c(2,3,4)), list(c(4,3,2), c(3,2,1))) B = list(list(c(1,2,3), c(2,3,4)), list(c(4,3,2), c(3,2,1))) Let's say I want to apply function(x, y) x + y to all the corresponding elements in A and B and preserve the nested structure. The desired result would be result = list

问题 I'm new to Hadoop and I'm trying to figure out how it works. As for an exercise I should implement something similar to the WordCount-Example. The task is to read in several files, do the WordCount and write an output file for each input file. Hadoop uses a combiner and shuffles the output of the map-part as an input for the reducer, then writes one output file (I guess for each instance that is running). I was wondering if it is possible to write one output file for each input file (so keep

问题 I'm new to Hadoop and I'm trying to figure out how it works. As for an exercise I should implement something similar to the WordCount-Example. The task is to read in several files, do the WordCount and write an output file for each input file. Hadoop uses a combiner and shuffles the output of the map-part as an input for the reducer, then writes one output file (I guess for each instance that is running). I was wondering if it is possible to write one output file for each input file (so keep

问题 I have a directory (Final Dir) in HDFS in which some files(ex :10 mb) are loading every minute. After some time i want to combine all the small files to a large file(ex :100 mb). But the user is continuously pushing files to Final Dir. it is a continuous process. So for the first time i need to combine the first 10 files to a large file (ex : large.txt) and save file to Finaldir. Now my question is how i will get the next 10 files excluding the first 10 files? can some please help me 回答1:

问题 I am new to Hadoop. I want to access a command line argument from main function(Java program) inside the map function of the mapper class. Please suggest ways to do this. 回答1: Hadoop 0.20, introduced new MR API, there is not much functionality difference between the new (o.a.h.mapreduce package) and old MR API (o.a.h.mapred) except that data can be pulled within the mappers and the reducers using the new API. What Arnon is mentioned is with the old API. Check this article for passing the