FeatureMerger

Example: Merging attributes and geometry to CSV data

In this example, we have two datasets - a CSV text file of historical crime reports, and a shapefile of public streets. Both of the datasets have one piece of information in common, that is an address in the form of “hundred” block.

The FeatureJoiner would likely be more effective to do a simple attribute value join, however, the format of the address is slightly different in each dataset. The CSV data uses the string “XX” in place of zeroes in the address:

And the street data has the more conventional form, with zeroes:

Our goal is to merge the street geometry onto the crime data - producing one output feature for each crime record. And so, The CSV data is routed into the Requestor input port, and the streets are routed into the Supplier port.

In the parameters dialog, we need to create a Join On pair of Requestor and Supplier values. As the format of the addresses is not identical, we will adjust one, constructing a key. With the assistance of the Text Editor, we create an expression that will replace the “XX” of the address with “00”, and so match the format of the street (Supplier) data.

The other half of the pairing is the attribute value HBLOCK from the street data.

Feature Merge Type is set to Attributes and Geometry. The default values for Attribute Accumulation (Merge Supplier) will provide the correct results.

The Merged output contains crime records, now with geometry for the street and associated street attributes. Note that the address format was not actually changed by the constructed expression - it was just used for matching evaluation. In this location, 137 crime records were found. Each one now has (identical) geometry.

To see this example reversed - attaching all crime records to a single street - see the next example.

Example: Many-to-one merging to create a list attribute

In this example, we reverse the scenario in the above example. We want to merge all the historical crime records onto the street data, producing one record per street line segment (block), with a list attribute containing the crime data.

In this case, the streets are the Requestor features, and the crime data is the Supplier.

In the parameters dialog, we again create a Join On pair, using an expression to match the two (slightly different) hundred block formats. The Feature Merge Type is Attributes Only, as the Requestors (streets) already have the desired geometry.

Process Duplicate Suppliers is enabled. Without this, the first match would be processed and the remainder discarded. A count of how many Suppliers (crimes) matched will be kept in the Number of Suppliers Attribute, named Incident_Count.

Generate List is enabled, and given the List Name of Crime_Records. We will add only Selected Attributes to the List, and choose TYPE and YEAR.

The Merged output features now have a list attribute, containing all matching records from the CSV. Note the Incident_Count attribute.

Joining Transformers Comparison Matrix

Transformer	Match By	Uses SQL Statements	Can Create List	Input Type	Notable	Description
FeatureJoiner	Attributes	No	No	Features	Best performance for simple joins on attribute values Cannot create lists - represents multiple joins as multiple output features Cannot use constructed keys or expressions	Joins features by combining the attributes and/or geometry of features based on common key attribute values. Performs the equivalent of Inner, Left, and Full SQL joins.
FeatureMerger	Attributes	No	Yes	Features	Can use expressions as keys (constructed keys) Can create lists – represents multiple joins as a list on a single feature Cannot match on geometry	Merges the attributes and/or geometry of one set of features onto another set of features, based on matching key attribute values and expressions.
ListBasedFeatureMerger	List Attribute to Single Attribute	No	Yes	Features	Only joining transformer to use all list attribute contents as keys (others may use one specific value in a list, but not the entire list)	Merges the attributes and/or geometry of one set of features onto another set of features, based on matching list attribute values with key attribute values and expressions.
InlineQuerier	SQL query	Yes	No	Features	Use SQL on non-SQL data Allows multiple join/SQL statements, and so can replace multiple transformers with one	Creates a set of SQLite database tables from incoming features, executes SQL queries against them, and outputs the results as features.
SQLCreator	SQL query	Yes	No	External DB	Best if all features already in SQL-capable source Read an external DB table mid-translation	Generates FME features from the results of a SQL query executed once against a database. One FME feature is created for each row of the results of the SQL query.
SQLExecutor	SQL query	Yes	No	External DB	Best for complex joins between features and SQL-capable source Read an external DB table mid-translation	Executes SQL queries against a database. One query is issued to the database for each initiating feature that enters the transformer. Both the initiating features and the results of the query may be output as features.
DatabaseJoiner	Attributes	No	Yes	External DB and Features	Best for simple joins between features and a database table Very efficient if keys indexed, and caches data locally Read an external DB table mid-translation Non-blocking	Joins attributes from an external table to features already in a workspace, based on a common key or keys. SQL knowledge not required. Non-blocking transformer.
Matcher	Geometry and/or Attributes	No	Yes	Features	The only one of these methods that can use geometry as key for matching Can look for attribute differences Uses geometry, not spatial relationships	Detects features that are matches of each other. Features are declared to match when they have matching geometry, matching attribute values, or both. A list of attributes which must differ between the features may also be specified. If matching on attributes only (not geometry), using the FeatureMerger or another method will give better performance.

Requestor

Features that will receive new attributes and/or geometry from the features connected to the Supplier port.

Supplier

The source of new attributes and/or geometry for features that enter through the Requestor port.

Note that by setting Process Duplicate Suppliers to Yes, more than one Supplier may be merged to each Requestor. These Suppliers potentially could come from different sources (such as different database tables).

Merged

Requestors that match a Supplier (or possible multiple Suppliers, if Process Duplicate Suppliers is set to Yes).

UnmergedRequestor

Requestors that do not match any Suppliers. If a Join On key is null or missing on a Requestor feature, that feature is output onto this port.

UsedSupplier

Suppliers that are found by at least one Requestor.

Note: A Supplier may still be output through this port even though none of its attributes were merged. This can occur because all of the attributes were already present in the Requestor or were provided by earlier Suppliers.

UnusedSupplier

Suppliers that do not match any Requestors. If a Join On key is null or missing on a Supplier feature, that feature is output onto this port.

If Process Duplicate Suppliers is No, then duplicate suppliers will be rejected. If Reject Null and Missing Keys is Yes, then keyless features will be rejected.

Rejected Feature Handling: can be set to either terminate the translation or continue running when it encounters a rejected feature. This setting is available both as a default FME option and as a workspace parameter.

Transformer

Group By

The input features may be partitioned by the Group By parameter. If you choose any Group By attributes, then references between features will only be resolved if they share a common value for the selected attributes.

If you do not choose any Group By attributes, all features are processed together.

If you have more than one Reader, a typical use is to group by reader_id to ensure that references are resolved within the correct set of features.

Suppliers First

When this option is enabled, the transformer will assume that all Suppliers will enter the transformer before any Requestors. Once the first Requestor arrives, it will process and output Requestors as they come in. The Suppliers will be output after all the Requestors have been processed.

Note: It is the user’s responsibility to make sure all the Suppliers arrive before the Requestors. The transformer will stop accepting Suppliers once it receives its first Requestor when this option is enabled.

Join On

Requestor

Specify an expression from the Requestor feature to match with the Supplier feature expression.

An expression can be a constant, attribute value, function or mixture. Leading and trailing space characters are trimmed from the evaluated expressions. Matches are made when the trimmed values of all the Requestor expressions equal the trimmed values of their corresponding Supplier expressions.

Supplier

Specify an expression from the Supplier feature to match with the Requestor feature expression.

An expression can be a constant, attribute value, function or mixture. Leading and trailing space characters are trimmed from the evaluated expressions. Matches are made when the trimmed values of all the Requestor expressions equal the trimmed values of their corresponding Supplier expressions.

Generally, the Suppliers will have expressions defined that result in a unique match with a Requestor, and any duplicate Suppliers are ignored by the transformer. However, if the Process Duplicate Suppliers parameter is set to Yes, then all Suppliers whose expressions match their corresponding Requestor expressions will be combined onto that Requestor.

Comparison Mode

The Comparison Mode column specifies how to perform the comparison between Requestor and Supplier attribute values. If Automatic or Numeric is specified, an attempt will be made to convert attribute values to numbers before comparing them.

Merge Parameters

Feature Merge Type

This parameter specifies what to merge onto the completed feature. Choices include:

Attributes Only: The Suppliers’ attributes will be joined to the attributes of the Requestor features.
Geometry: Supplier geometry will replace Requestor geometry.
Attributes and Geometry: Both the geometry and attributes from the Suppliers are joined to the Requestor features. Any geometry on the Requestor will be overwritten.

Reject Null and Missing Keys

Yes: Any Requestor or Supplier feature that contains a null or missing join key is output via the <Rejected> port.

No: Null and missing keys are treated as empty strings.

Process Duplicate Suppliers

If more than one Supplier is found for a given Requestor, and Process Duplicate Suppliers is not enabled, then every Supplier after the first is output via the <Rejected> port and only the first of the Suppliers will be matched with a Requestor.

If Process Duplicate Suppliers is enabled, duplicate Suppliers are all matched with the corresponding Requestor. Attributes are merged based on the Attribute Accumulation mode, and optionally output as a list attribute of the Requestor, using the specified List Name. The Supplier geometry is merged using the specified Geometry Merge Type.

Geometry Merge Type

Specifies how to merge duplicate Suppliers onto the Requestor. It is applicable only if Feature Merge Type specifies to merge geometry. Choices include:

Build Polygons: If the Suppliers consist exclusively of polygon and donut polygon features, any common border segments will be removed. If the Suppliers contain at least one non-donut or non-polygon feature, then the transformer will form polygons and donuts from the Suppliers and will join connected line segments of the Supplier features before setting the geometry of the Requestor feature. In this case, the geometry may be an aggregate if several disjoint geometries were created.
Build Aggregates: The transformer will create an aggregate of the geometries of the Supplier features. (If there is only one Supplier feature, then the Requestor geometry will be an aggregate with one element.)
Build Lines from Points: The transformer will connect the points of the Supplier features into lines. Note that any non-point features that are referenced will be ignored when building lines.

Tolerance

The minimum distance between geometries in 2D before they are considered equal, in ground units. If the tolerance is None, the geometries must be exactly identical to be considered equal. If the tolerance is Automatic, a tolerance will be automatically computed based on the location of the input geometries. Additionally, a custom tolerance may be used.

Connect Z Mode

If applicable, select a method for handling z values.

Connect Z Mode

When viewed in 2D (ignoring Z), a path (which may define the border of a polygon) may appear to be closed as shown in the left figure below. This same path, when viewed in 3D, may appear to be open as shown in the right figure below.

To specify how (and if) paths should be closed in 3D, select one of the listed modes.

Mode	Description	Example
Extend	The Curve is extended so that all vertices are left at their original location.
Average	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is the average of the original two.
First Wins	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is taken from the first encountered vertex.
Last Wins	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is taken from the last encountered vertex.
Ignore	Z values are ignored. No change is made to the way the nodes are connected.

Number of Suppliers Attribute

The name of an attribute which will store a count of the number of Suppliers matched a Requestor.

Attribute Accumulation

If attributes on the Supplier and Requestor feature share the same name, but are not geometry attributes that start with fme_, then they are deemed conflicted.

Accumulation Mode	Merge Supplier: The Requestor feature will retain all of its own un-conflicted attributes, and will additionally acquire any un-conflicted attributes that the supplier feature has. This mode will handle conflicted attributes based on the Conflict Resolution parameter. Prefix Supplier: The Requestor feature will retain all of its own attributes. In addition, the Requestor will acquire attributes reflecting the supplier feature’s attributes, with the name prefixed with the Prefix parameter. Only Use Supplier: The Requestor feature will have all of its attributes removed, except geometry attributes that start with fme_. Then, all of the attributes from one (arbitrary) supplier feature will be placed onto the Requestor.
Conflict Resolution	Use Requestor: If a conflict occurs, the Requestor values will be maintained. Use Supplier: If a conflict occurs, the values of the supplier will be transferred onto the Requestor.
Ignore Nulls	No: Treat null attribute values like other attribute values. Yes: Treat null attribute values as less important than other attribute values. Whenever a null value is merged with a non-null value, the non-null value shall prevail, regardless of what Conflict Resolution is set to. Note: Null and other attribute values are always more dominant than missing attribute values. That is, whenever an attribute value is merged with a missing attribute value, the attribute value shall prevail, regardless of the Ignore Nulls and Conflict Resolution settings.
Prefix	To prevent a Supplier attribute from being ignored because the Requestor attribute already exists, you can optionally specify a prefix that will be applied to each Supplier attribute when it is added to the Requestor. When there are multiple Supplier features for a Requestor feature, multiple Supplier attribute values are merged into the same prefixed attribute. When multiple Supplier features have the same attribute, generally the resulting attribute value is taken from the last of these features. However, this process is governed by the Ignore Nulls parameter.

Generate List

If there are duplicate Suppliers and Generate List is enabled, then any Suppliers that are combined with a Requestor will have their attributes added to the specified list on the Requestor.

Note: List attributes are not accessible from the output schema in Workbench unless they are first processed using a transformer that operates on them, such as ListExploder or ListConcatenator. All list attribute transformers are displayed in the Contents pane of the Transformer Help under Lists. Alternatively, AttributeExposer can be used.

List Name

Enter a name for the list attribute.

Add To List

All Attributes: Every attribute from a Supplier that combined with a Requestor will be added to the list specified in List Name.

Selected Attributes: Only the attributes specified in the Selected Attributes parameter will be added to the list specified in List Name.

Selected Attributes

The attributes to be added to the list when Add To List is Selected Attributes.

How to Set Parameter Values

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more - whether entered directly in a parameter or constructed using one of the editors.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Working with User Parameters	Create your own editable parameters.

Related Transformers

DatabaseJoiner

FeatureJoiner

InlineQuerier

ListBasedFeatureMerger

SQLCreator

SQLExecutor

Matcher

Processing Behavior	Group-Based
Feature Holding	Yes
Dependencies	None
FME Licensing Level	FME Base Edition and above
Aliases
History
Categories	Filters and Joins

FeatureMerger

Typical Uses

How does it work?

Usage Notes

Choosing a Feature Joining Method

Configuration

Input Ports

Output Ports

Parameters

Editing Transformer Parameters

Defining Values

Reference

FME Knowledge Center