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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.

653 questions
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Hadoop: Do Mappers run parallel When we use NLineInputFormat?

If yes, How does HDFS split input file into N lines to read by per mapper ? I believe It's impossible! When the splitter needs offset or bytes to split, It can be possible to split without processing whole of input file. But when the number of '\n'…
beginner1010
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Hadoop Map-Reduce , Need to combine two mapper with one common Reducer

I need to implement below Functionality using Hadoop Map-Reduce? 1) I am reading one input for a mapper from one source & another input from another different input source. 2) I need to pass both output of mapper into a single reducer for further…
HarshaKP
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How does Mapper class identify the SequenceFile as inputfile in hadoop?

In my one MapReduce task, I override the BytesWritable as KeyBytesWritable, and override the ByteWritable as ValueBytesWritable. Then I output the result using SequenceFileOutputFormat. My question is when I start the next MapReduce task, I want to…
JoJo
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Mapper between json and php class

I'm starting a new project that uses couchbase (a noSQL database that stores objects in json format), together with php. The thing is that it would be really easy to work with them both if I could have something that maps json into one of my own php…
ThisIsErico
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How to create String primary Key in lift's Mapper ORM?

How can we create a mapper with string as it's primary key in lift's Mapper ORM ?
vkantiya
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Is there a generic way of setting field values in mapper from list of values?

Is there a way of creating method for setting the value in the Model's fields without setting the values explicitly like - ModelName.create.fieldName1("value").fieldName2("value2") and so on Can we iterate through all available fields of that…
vkantiya
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How to return 1 if the first letter of a word is a vowel, return 0 otherwise. Mapper (MapReduce) problem

This is the first part of a MapReduce problem I am working on. I need a function that yields 1 if the first letter of a word starts with a vowel, otherwise it should yield 0. The program is run in the terminal by piping a text file to the mapper…
Zaku
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Mapper Mapster - How to unit test config?

I come here because i dont find the answer online :/ I would like to test my configuration of Mapster to avoid miss mapping which happens at developpement time. But i dont find how to implement that with Mapster lib. Any clue ? Regards,
Wazzouille
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Can't find related Attribute using Mapstruct Spring Boot

I am following the following document for implementing a mapper interface: MapStruct- Baeldung for Employee and EmployeeDTO. Here is my Employee Class: public class Employee { private int id; private String name; // getters and setters } Here is my…
amangupta
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MapStruct using default constructor over parameterised constructor of Kotlin data class(error: constructor in class cannot be applied to given types)

In my Micronaut Kotlin project I have two repositories. I am using MapStruct in both of them. Source Class @JsonInclude data class Source( var id: String, var no: String, var value: String, ) Destination Class @JsonInclude data class…
Sankalp Bhatt
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How to properly map Entity Framework entities to DTO and vice-versa?

In the data access level, I have defined such an entity: public class Instagram { public int Id { get; set; } public string Username { get; set; } = null!; public string Password { get; set; } = null!; public string? StateData { get;…
Егор Лазеба
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Single map task taking long time and failing in hive map reduce

I am running a simple query like the one shown below(similar form) INSERT OVERWRITE table TABLE2 PARTITION(COLUMN) SELECT * FROM TABLE1 There is nothing wrong with query syntax wise. TABLE2 IS EMPTY and the total size of TABLE1 is 2gb in…
SuperAadi
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Can't import the named export 'MapperKind' from non EcmaScript module

I made a query and useUser function as below: const ME_QUERY = gql` query me { me { username avatar } } `; function useUser() { const isLoggedIn = useReactiveVar(isLoggedInVar); const { data, error } = useQuery(ME_QUERY,…
Hayat
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The fault tolerance in Mapreduce when map worker fail

Recently I was reading Google's paper, "MapReduce: Simplified Data Processing on Large Clusters". The words below confuse me. It says When a map task is executed first by worker A and then later executed by worker B (because A failed), all workers…
Snoopy
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Get custom attribute from LDAP and map into keycloak

we are using synchronize function to get all users from LDAP into keycloak. I want to get custom attribute "User logon name" which is available in LDAP. mapper setting which is already done is getting username, first name, last name, mail. how do i…
veer kumar rathore
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