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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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GWT POJO-JSON Mappers?

I was looking to find a GWT POJO-JSON mapper. In responses to another question and by Googling around I found following solutions: GWT Overlay Types GWT AutoBean piriti gwtprojsonserializer gwt-jsonizer My question is that does any of these (or…
Ali Shakiba
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Cassandra insert preparedStatement or mapper?

We are doing inserts of a few millions records in 1 time in a Cassandra 3.0 database. Question is : what has best performance: using the mapper (annotating our object 'JPA' style) or using a prepared statement, which will only be prepared once and…
chnoe
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Unzip files in the directory they are in with Ant

This should be simple but I can't find a way to do it. I need to extract any zip files in sub directories of a directory to the same sub directory using Ant. The files are passed to the ant task as a fileset with wildcards e.g. */.zip. For example,…
Stefg
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When does a mapper store its output to its local hard disk?

I know that The output of the Mapper (intermediate data) is stored on the Local file system (not HDFS) of each individual mapper data nodes. This is typically a temporary directory which can be setup in config by the Hadoop administrator. Once the…
Neha Sharma
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how to decrease the number of mapper in hive while the file is bigger than block size?

guys I have a table in hive which have more than 720 partitions，and in each partition there is more than 400 files and the file's average size is 1G. Now I execute following SQL: insert overwrite table test_abc select * from DEFAULT.abc A WHERE…
lance
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Orika mapper - map to List

I have one object with the field List and I want to map it to a second object with field List. I need to map 2 objects. I can not find the way. Situation map class One -> class Two : public class One { String field11; …
matrezz
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TinyMapper: bind using expression

Current code throw exception Expression is not a MemberExpression: TinyMapper.Bind(cfg => { cfg.Bind(x => $"{AppSettings.AvatarBaseUrl}/{x.AvatarUrl}", t => t.AvatarUrl); }); Is there a way i could…
Maxim Zhukov
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What is the `connection` parameter of MapperExtension in sqlalchemy?

The class MapperExtension has some methods, and before_insert, before_update, ... all have a parameter connection. def before_insert(self, mapper, connection, instance): I've read the documents of MapperExtension, but found nothing about this…
Freewind
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Hadoop - Properly sort by key and group by reducer

I have some data coming out from the reducer which are like this : 9,2 3 5,7 2 2,3 0 1,5 3 6,3 0 4,2 2 7,1 1 And I would like to sort them according to the number on the second column. Like this : 2,3 0 6,3 0 7,1 1 5,7…
Robin Dupont
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hazelcast mapper class not found

I`m trying to run map/reduce task on hazelcast 3.4, but I keep getting classs not found exception I created several players and store them to IMap this.conf = new ClientConfig(); HazelcastInstance cluster =…
zlosim
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How to "unset" injectableValues from objectMapper?

i am using injectableValues to deserealize a json. I am doing this like: final InjectableValues.Std injectableValues = new InjectableValues.Std(); injectableValues.addValue(HttpRestResponse.class, response); emailsResponse =…
jscherman
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AutoMapper IDataReader Mapping default value to entity

im using AutoMapper for map entity and DataSet AutoMapper.Mapper.CreateMap(): and i have a property call MobileNumber in Home entity and want to map static value for this property in entity so how can i add static value when…
LittleDragon
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Dependency Injection in Hadoop Mapper

I want to inject a dependency inside my Mapper class. Example Mapper Class: public class Mapper() { private MyInterface myObject; public void map() { // Map code here } } I would like to inject an implementation of…
Water
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How does MapReduce process multiple input files?

So I'm writing a MR job to read hundreds of files from an input folder. Since all the files are compressed, so instead of using the default TextInputFormat, I was using the WholeFileReadFormat from an online code source. So my question is that does…
user1453951
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How to automatically create concrete classes based on field value

Consider this example: Database (similar to Stackoverflow) has a table with questions and answers in the same table distinguishable by PostType field. I would like to get back a list of lastest posts be it questions or answers. As questions and…
Robert Koritnik
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