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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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Can Hadoop mapper produce multiple keys in output?

Can a single Mapper class produce multiple key-value pairs (of same type) in a single run? We output the key-value pair in the mapper like this: context.write(key, value); Here's a trimmed down (and exemplified) version of the Key: import…
Monis Iqbal
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MapStruct: How to map property from "java.lang.Object to "java.lang.String"

New to MapStrut; Object to String Error: [ERROR] /util/LicenseMapper.java:[11,23] Can't map property "java.lang.Object license.customFields[].value" to "java.lang.String license.customFields[].value". Consider to declare/implement a mapping method:…
fatherazrael
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Cannot convert a valid UUID string to UUID using mapper.readValue

I have a valid UUID in string format 7a041f81-1214-41e5-bb58-9a46b2ca08d4 but when I user a ObjectMapper to convert it to a UUID I keep getting this error. UUID uuid =…
user11311618
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How to fix The mapper function returned a null value." error in Java / RxJava2 Null?

I hava some problem with RxJava2 and a stream (Observable and Observer) Actually, my stream return an error The mapper function returned a null…
user11391492
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CSVHelper how to map a string to object

I have a string in a variable, rather than in a file. Can I use the CSVHelper (https://joshclose.github.io/CsvHelper/) to parse the string and map it onto my object? The code to map a CSV file works: TextReader reader = new…
Mark Tait
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Correct way to unit test a Mapper transformation method

I have a Mapper class with one method which transforms one type of User to another type of User: /** * Transform new {@link User} to legacy {@link com.xxx.xxx.bo.bean.User}. * @param user User to transform. * @return Transformed user. * @throws…
svprdga
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how to exclude whole property if they are null from Modelmapper

Does ModelMapper(http://modelmapper.org/) support what exclude property? If the value is null. I just found PropertyMap out. but It is a constraint to me. because I have to describe a specific property that I want. Like this. ModelMapper…
Brady
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Bad grammar SQL Exception while reading the values using rowmapper

This is my Model class //Model public class CustomerData { private String locomotive_id; private String customer_name; private String road_number; private String locomotive_type_code; private String…
Santosh Anantharamaiah
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What's wrong with comparing non-optional bool in a single if structure in swift

I have been coding in Swift for a while, and I think I had to put a ! on all my let field variables that were not defined immediately. Now I notice today that this piece of code does not compile and I am really surprised? why is this? class MyClass…
jsgoupil
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How do I flatten the top level folder of a zip file with ant?

A lot of zip files have a root folder, how do I unpack the zip file and get rid of the root folder? I know there is the globmapper: …
flavio.donze
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when is an identity mapper/reducer used?

I had two conceptual doubts related to mapreduce and hadoop.I know a simple one iteration map-reduce program, know what a mapper,reducer, shuffler is.. But still want to know about the following questions 1)when is iterative map reduce done? 2)i…
pranav shah
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Job and Task Scheduling In Hadoop

I am little confused about the terms "Job scheduling" and "Task scheduling" in Hadoop when I was reading about delayed fair scheduling in this slide. Please correct me if I am wrong in my following assumptions: Default scheduler, Capacity scheduler…
GoT
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BO <=> DTO mapper in Java

I am currently in my application maping DTOs to BO (and vice versa) manually. However, this approach is awkward and clumsy. Is there any good mapper between these two representations? My requirements follow: Should support conversion of JPA…
malejpavouk
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ApplicationError: 7 when processing is done for mapreduce worker writing to Google Cloud Storage

Just finishing up a large Appengine mapreduce task, and many of my shards are stuck moments from the finishline. Here's the setup: filenames = yield mapreduce_pipeline.MapperPipeline( 'example mapper name', …
Ipsquiggle
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Is there any bulkUpdate (similar to bulkDelete_!!) in Mapper?

Is there a bulkUpdate method similar to bulkDelete_!! in mapper so that i can update records in underlying table ?
vkantiya
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