tAggregateRow - 6.1

Talend Open Studio for Big Data Components Reference Guide

EnrichVersion
6.1
EnrichProdName
Talend Open Studio for Big Data
task
Data Governance
Data Quality and Preparation
Design and Development
EnrichPlatform
Talend Studio

Function

tAggregateRow receives a flow and aggregates it based on one or more columns. For each output line, are provided the aggregation key and the relevant result of set operations (min, max, sum...).

Purpose

Helps to provide a set of metrics based on values or calculations.

tAggregateRow properties

Component family

Processing

 

Basic settings

Schema and Edit Schema

A schema is a row description. It defines the number of fields (columns) to be processed and passed on to the next component. The schema is either Built-In or stored remotely in the Repository.

Click Edit schema to make changes to the schema. If the current schema is of the Repository type, three options are available:

  • View schema: choose this option to view the schema only.

  • Change to built-in property: choose this option to change the schema to Built-in for local changes.

  • 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.

 

 

Built-In: You create and store the schema locally for this component only. Related topic: see Talend Studio User Guide.

 

 

Repository: You have already created the schema and stored it in the Repository. You can reuse it in various projects and Job designs. Related topic: see Talend Studio User Guide.

 

Group by

Define the aggregation sets, the values of which will be used for calculations.

 

 

Output Column: Select the column label in the list offered based on the schema structure you defined. You can add as many output columns as you wish to make more precise aggregations.

Ex: Select Country to calculate an average of values for each country of a list or select Country and Region if you want to compare one country's regions with another country' regions.

 

 

Input Column: Match the input column label with your output columns, in case the output label of the aggregation set needs to be different.

 

Operations

Select the type of operation along with the value to use for the calculation and the output field.

 

 

Output Column: Select the destination field in the list.

 

 

Function: Select the operator among: count, min, max, avg, sum, first, last, list, list(objects), count(distinct), standard deviation.

 

 

Input column: Select the input column from which the values are taken to be aggregated.

 

 

Ignore null values: Select the check boxes corresponding to the names of the columns for which you want the NULL value to be ignored.

Advanced settings

Delimiter(only for list operation)

Enter the delimiter you want to use to separate the different operations.

 

Use financial precision, this is the max precision for "sum" and "avg" operations, checked option heaps more memory and slower than unchecked.

Select this check box to use a financial precision. This is a max precision but consumes more memory and slows the processing.

Warning

We advise you to use the BigDecimal type for the output in order to obtain precise results.

 

Check type overflow (slower)

Checks the type of data to ensure that the Job doesn't crash.

 

Check ULP (Unit in the Last Place), ensure that a value will be incremented or decremented correctly, only float and double types. (slower)

Select this check box to ensure the most precise results possible for the Float and Double types.

 

tStatCatcher Statistics

Check this box to collect the log data at component level. Note that this check box is not available in the Map/Reduce version of the component.

Global Variables

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.

Usage

This component handles flow of data therefore it requires input and output, hence is defined as an intermediary step. Usually the use of tAggregateRow is combined with the tSortRow component.

Log4j

If you are using a subscription-based version of the Studio, 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.

Limitation

n/a

Scenario: Aggregating values and sorting data

The following scenario describes a four-component Job. As input component, a CSV file contains countries and notation values to be sorted by best average value. This component is connected to a tAggregateRow operator, in charge of the average calculation then to a tSortRow component for the ascending sort. The output flow goes to the new csv file.

  • From the File folder in the Palette, drop a tFileInputDelimited component to the design workspace.

  • Click the label and rename it as Countries. Or rename it from the View tab panel

  • In the Basic settings tab panel of this component, define the filepath and the delimitation criteria. Or select the metadata file in the repository if it exists.

  • Click Edit schema... and set the columns: Countries and Points to match the file structure. If your file description is stored in the Metadata area of the Repository, the schema is automatically uploaded when you click Repository in Schema type field.

  • Then from the Processing folder in the Palette, drop a tAggregateRow component to the design workspace. Rename it as Calculation.

  • Connect Countries to Calculation via a right-click and select Row > Main.

  • Double-click Calculation (tAggregateRow component) to set the properties. Click Edit schema and define the output schema. You can add as many columns as you need to hold the set operations results in the output flow.

  • In this example, we'll calculate the average notation value per country and we will display the max and the min notation for each country, given that each country holds several notations. Click OK when the schema is complete.

  • To carry out the various set operations, back in the Basic settings panel, define the sets holding the operations in the Group By area. In this example, select Country as group by column. Note that the output column needs to be defined a key field in the schema. The first column mentioned as output column in the Group By table is the main set of calculation. All other output sets will be secondary by order of display.

  • Select the input column which the values will be taken from.

  • Then fill in the various operations to be carried out. The functions are average, min, max for this use case. Select the input columns, where the values are taken from and select the check boxes in the Ignore null values list as needed.

  • Drop a tSortRow component from the Palette onto the design workspace. For more information regarding this component, see tSortRow properties.

  • Connect the tAggregateRow to this new component using a row main link.

  • On the Component view of the tSortRow component, define the column the sorting is based on, the sorting type and order.

  • In this case, the column to be sorted by is Country, the sort type is alphabetical and the order is ascending.

  • Drop a tFileOutputDelimited from the Palette to the design workspace and define it to set the output flow.

  • Connect the tSortRow component to this output component.

  • In the Component view, enter the output filepath. Edit the schema if need be. In this case the delimited file is of csv type. And select the Include Header check box to reuse the schema column labels in your output flow.

  • Press F6 to execute the Job. The csv file thus created contains the aggregating result.