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Questions tagged [mapper]

The mapper is the first step in MapReduce framework, a component of a larger scalable, parallel-izable algorithm.

Maps input key/value pairs to a set of intermediate key/value pairs.

Maps are the individual tasks which transform input records into a intermediate records. The transformed intermediate records need not be of the same type as the input records. A given input pair may map to zero or many output pairs.

The most common map reduce framework is Apache Hadoop.

See also MapReduce Wiki.

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How to use Entity, Mapper, Service and Hydrator in ZF2

I am making a ZF2 app. I am using entities, mappers and services (e.g. UserEntity, UserMapper, UserService) to manage the objects/models. Properties in the entities are CamalCased (e.g. FirstName, LastName) while in the database, fields are using…
J Morgan
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Input/Output flow in map reduce chaining

i need help regarding map reduce chaining.i have a map reduce chain like this map->reduce->map i want the output of reducer to be used in the last mapper for example, in my reducer i am getting the max salary of an employee and this value is…
user1585111
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mapper behaving differently on local and on the cluster

I run a map only job(on Hadoop) in order to sort the key values, because it's said "Hadoop automatically sorts data emitted by mappers before being sent to reducers". input file 2013-04-15 835352 2013-04-16 846299 2013-04-17 …
likeaprogrammer
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Show in lineEdits the fields when click a row in a TableView

i have a CRUD form (more or less) in c++ with lineEdits and Labels upside, and a TableView down. Both have the same QSqlRelationalTableModel. I understood the "A Simple Widget Mapper" example, but how can i do a integration between the TableView and…
bluesky777
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Struts2 Restful Mapping configuration

I'm new in struts2, I tried to use Restful but I can't config. I have 2 Controllers: UsersController @Namespace("/api") public class UsersController extends ActionSupport implements ModelDriven…
Luc
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is the cleanup() method called for failed map tasks?

Is the cleanup() method called for failed map tasks? If so, how it ensures 'atomicity'? In my case, am preparing some statistics in mapper which are written to DB in the cleanup() method. In this case, if a mapper fails in the mid of executing…
RGC
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Jackson JSON read and write JSON String

I have i class (A) composed by an int and a List of my another object (B) composed only by int. They are all relative getters and setters method. I can save correctly my firts object into a String but i have problem while try reading it. If the…
user2520969
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In MapReduce how do you stop a reducer after processing X records

I am using Mapper to load a large amount of data which has the execution time and a large query associated with it.. I just need to find the 1000 most expensive queries, so i feed the execution time as the key to the output of my mapper. I use 1…
mm93rc213v
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Compound PrimaryKey in Mapper

I'm actually working with scala lift. I need to set a compound PK with Mapper, and from what I saw in the web (links below) its not possible. How can I do this? Links: How to create Composite-key for a Model in lift's…
user2502541
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Can I set the input a Mapper as a hashMap instead of an input file

I'm trying to setup a MapReduce task that utilizes the Parallel Scan feature by dynamodb. Basically, I want each Mapper class to take a tuple as the input value. Every example I've seen so far sets this : FileInputFormat.addInputPath(job, new…
n915
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the type must implement the inherited abstract method Reducer.reduce(Object, Iterator, OutputCollector, Reporter)

I am new to Hadoop, and this is my first Hadoop program. I am trying to create a Mapper class called WordMapper, but it throws be the below error. The type WordMapper must implement the inherited abstract method Mapper.map(Object, Object,…
Uday
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Can a 'ViewModel' hold 'DomainModel' type property

In asp.net MVC 4, I have 2 DomainModels Product Order and a related ViewModel OrderDetailsViewModel In my "OrderDetailsViewModelMapper" mapper file I am manually mapping these 2 DomainModels to my ViewModel. Mapper file…
Jaish Mathews
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Decoding a binary raster GIS file: Vertical Mapper .grd

Does anyone know of a method to decode this sort binary file. It should have a quite simple structure, a couple of lines of headers and then just grid data. I have the Vertical Mapper software but I want to cut out a step in my modelling process and…
Alex Byasse
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Accesing local filesystem without uploading to hdfs

Is there anyway to specify the inputpath in Hadoop outside the HDFS, I am running a single node cluster and want to access files outside the HDFS, so is there any way to do this???
Aparajith Chandran
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Hadoop program without reading contents of the file

It maybe a basic question but in the map reduce program, I would like to read the names of all the files present in the inputfolder rather than the contents and i would like to send the names of those files to my mapper class. Configuration…
Aparajith Chandran
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