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Component family
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Big Data / Hadoop
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Function
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This component allows you to group the original data by column and
add one or more additional columns to the output of preceding
grouped data.
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Purpose
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The tPigAggregate component adds
one or more additional columns to the output of the grouped data to
create data to be used by Pig.
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Basic settings
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Schema and Edit
Schema
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A schema is a row description. It defines the number of fields to be processed and passed on
to the next component. The schema is either Built-In or
stored remotely in the Repository.
Since version 5.6, both the Built-In mode and the Repository mode are
available in any of the Talend solutions.
Click Edit schema to make changes to the schema. If the
current schema is of the Repository type, three options are
available:
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View schema: choose this option to view the
schema only.
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Change to built-in property: choose this option
to change the schema to Built-in for local
changes.
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Update repository connection: choose this option to change
the schema stored in the repository and decide whether to propagate the changes to
all the Jobs upon completion. If you just want to propagate the changes to the
current Job, you can select No upon completion and
choose this schema metadata again in the [Repository
Content] window.
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Built-in: The schema will be
created and stored locally for this component only. Related topic:
Talend Studio User Guide.
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Repository: The schema already
exists and is stored in the Repository, hence can be reused in
various projects and Job designs. Related topic: see
Talend Studio User Guide.
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Group by
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Click the plus button to add one or more columns to set tuples in
the source data as group condition.
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Operations
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Click the plus button to add one or more columns to generate one
or more additional output columns based on conditions:
Additional Output Column: Select a
column in the original data as output column.
Function: Functions for operation
on input data.
Input Column: Select a column in
the original data as input column.
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Advanced settings
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Increase parallelism
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Select this check box to set the number of reduce tasks for the
MapReduce Jobs.
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tStatCatcher Statistics
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Select this check box to gather the Job processing metadata at the
Job level as well as at each component level.
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Global Variables
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ERROR_MESSAGE: the error message generated by the
component when an error occurs. This is an After variable and it returns a string. This
variable functions only if the Die on error check box is
cleared, if the component has this check box.
A Flow variable functions during the execution of a component while an After variable
functions after the execution of the component.
To fill up a field or expression with a variable, press Ctrl +
Space to access the variable list and choose the variable to use from it.
For further information about variables, see Talend Studio
User Guide.
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Usage
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This component is commonly used as intermediate step together with
input component and output component.
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Prerequisites
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The Hadoop distribution must be properly installed, so as to guarantee the interaction
with Talend Studio. The following list presents MapR related information for
example.
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Ensure that you have installed the MapR client in the machine where the Studio is,
and added the MapR client library to the PATH variable of that machine. According
to MapR’s documentation, the library or libraries of a MapR client corresponding to
each OS version can be found under MAPR_INSTALL
hadoophadoop-VERSIONlib
ative. For example, the library for
Windows is lib
ativeMapRClient.dll in the MapR
client jar file. For further information, see the following link from MapR: http://www.mapr.com/blog/basic-notes-on-configuring-eclipse-as-a-hadoop-development-environment-for-mapr.
Without adding the specified library or libraries, you may encounter the following
error: no MapRClient in java.library.path.
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Set the -Djava.library.path argument, for example, in the Job Run VM arguments area
of the Run/Debug view in the [Preferences] dialog box. This argument provides to the Studio the
path to the native library of that MapR client. This allows the subscription-based
users to make full use of the Data viewer to view
locally in the Studio the data stored in MapR. For further information about how to
set this argument, see the section describing how to view data of Talend Big Data Getting Started Guide.
For further information about how to install a Hadoop distribution, see the manuals
corresponding to the Hadoop distribution you are using.
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Log4j
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The activity of this component can be logged using the log4j feature. For more information on this feature, see Talend Studio User
Guide.
For more information on the log4j logging levels, see the Apache documentation at http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html.
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Limitation
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Knowledge of Pig scripts is required.
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