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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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Getting the exception in WordCount Program in Hadoop

I am facing this exception when trying to run the first program on hadoop. (I am using hadoop new API on version 0.20.2). I searched on web, it looks like most of the people faced this problem when they did not set MapperClass and ReducerClass in…
KBR
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Connecting Database from lift app using mapper error

I am trying to connect my lift app to the database. i have the following code to do the operation. i have downloaded and included the lift-mapper_2.9.1 to my app and i have given the following code in boot.scala import…
isc
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hadoop mapper reading multiple lines

New to hadoop - I am trying to read in my HDFS file in chunks, for example - 100 lines at a time and then running regression with the data using apache OLSMultipleLinearRegression in the mapper. I am using this code shown here to read in multiple…
cs_newbie
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dependency injection with multiple calls to database

I am trying to better implement OOP and dependency injection in my code and come across the below issue. I provide services to clients where an employer and a company are involved (with corresponding models, mappers and database tables): class…
tihe
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Adding not-yet-saved objects to MappedManyToMany

The project I am working on has run into some undesirable Mapper behaviour. It seems you cannot add objects to many-to-many associations unless the objects are already saved in the database (more specifically, you cannot retrieve some not-saved…
frig.neutron
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Using Jackon ObjectMapper to map to array of classes, alongside other fields?

I have some Json in the following form: "items": [ { "id": 1, "text": "As a user without a subscription, I get a choice of available ones.", "status": "finished", "tags": [ { "id": 1234, "name": "feature=subs" }, { …
Joe
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In hadoop how do you print within the "configure()" method?

In the bottom example in this hadoop tutorial there is a "configure()" method. http://hadoop.apache.org/common/docs/r0.20.2/mapred_tutorial.html#Source+Code-N10FD0 I wanted to put a print statement within it to know that it arrives there. However,…
DSH
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How does the object in class pattern work, as used in the Lift Framework?

I'm new to scala and can't get my head around how the Lift guys implemented the Record API. However, the question is less about this API but more about Scala in general. I'm interested in how the object in class pattern works, used in Lift. class…
Otto
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What vaue to be set for mappers and reducers while executing jobs in hadoop and how to decide it?

I am running Hive jobs on hadoop cluster. I just came to know to know that the performance will get improve/change if you just concentrate on different behavior mapper and reducer. But I haven't played with it until. Until no I just played with Hive…
Bhavesh Shah
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How to increase the mappers and reducers in hadoop according to number of instances used to increase the performance?

If I increase the number of mappers and decrease the number of reducers, then is there any difference in the performance (increase/decrease) of any job while execution? Also I want to ask that How to set the number of mappers and reducers? I have…
Bhavesh Shah
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reading a matrix in hadoop map reduce

hi i have a matrix and want to pass it on to mapper class in hadoop multinode cluster set up, but matrix is not in file. Is there any way of passing matrix without writing it to a file?
mahashwetha
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What is the benefit of assigning a variable of a Mapper Instance to be static?

Let's suppose I have a Mapper Interface as follows: public interface SomeMapper { SomeMapper INSTANCE = Mappers.getMapper(SomeMapper.class); //Some Random Method public RandomResponse doSomething(); } And then I have an Executor…
RandomGuy
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does anyone know how history mapper works in python?

does anyone know how history mapper works in python? Why are NOT all fields of the main table written to the history table? example: class TableNameOrm(DbNameMetaBase, MixinLocked, MixinCreatedAt, Versioned): __tablename__ = 'table_name' id…
Sergey R
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Exclude colums (fields) using Jackson CsvMapper to serialize POJO

I have a Java class and i want to serialize it into CSV using jackson. In addition i want to exclude from the csv a single field base on a external property. I have tried using all features provides by jackson like Feature.IGNORE_UNKNOWN=true or…
Sabbullo
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Map-only job is not running. Stuck at Running job

I have streamed data through Apache Flume and the data has been stored in a temp file in my hdfs folder at: user/*****/tweets/FlumeData.1643626732852.tmp Now I am trying to run a mapper only job which will be pre-processing the job by way of url…
Daremitsu
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