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GeoProcessor / Command / For

Overview

The For command iterates through a block of commands between For and matching EndFor commands. A processor property is set to the value of the iteration property and can be used by other commands that support properties, using the ${Property} notation. For commands can iterate over:

  • a list of supplied values (specify using ListProperty parameter)
  • a sequence of integers or floating-point double precision numbers specified with start (SequenceStart parameter), end (SequenceEnd parameter), and increment (SequenceIncrement parameter)
  • values from a Table column

For commands can be nested. Status messages for the run mode are accumulated in each command. A limitation of using For with properties is that the command when edited may show GeoLayer identifiers and other command parameters as ${Property} values, rather than actual data, because the values get expanded at run-time. This provides increased processing power but errors may not be evident until commands are run.

Command Editor

The following dialog is used to edit the command and illustrates the command syntax.

For

For Command Editor (see full-size image)

Command Syntax

The command syntax is as follows:

For(Parameter="Value",...)

Command Parameters

Parameter                      Description Default                 
Name
required		 The name of the for loop, which will be matched with the name of an EndFor command to indicate the block of commands in the loop. None - must be specified.
IteratorProperty The processor property that will be set to the iterator property. The object type will depend on that used to provide the iteration property list. For example, if a sequence of integers is being iterated, the property will contain an integer. Same as Name.
If iterating over a LIST ...
ListProperty Specify if the list is iterating over a property that contains a list of strings. Specify this or Sequence* parameters.
If iterating over a SEQUENCE ...
SequenceStart Starting value when a sequence is specified for iteration, an integer or floating-point number (with decimal). No default if sequence is used.
SequenceEnd Ending value when a sequence is specified for iteration, an integer or floating-point number (with decimal). No default if sequence is used.
SequenceIncrement Increment for sequence iterator. 1 or 1.0 depending on type for SequenceStart.
If iterating over a TABLE ...
TableID The table identifier, when specifying the iterator as a column from a table. ${Property} syntax is recognized. No default if table is used.
TableColumn The table column name, when specifying the iterator as a column from a table. ${Property} syntax is recognized. No default if table is used.
TablePropertyMap Specify the names of column names and corresponding processor property names to set. This allows other commands to access the values of those properties using ${Property} syntax.

Specify using format:
ColumnName1:PropertyName1,ColumnName2:PropertyName2		 None - only the iterator column value will be set as a property using IteratorProperty.

Examples

See the automated tests.

Example to process data for a list of counties

This simple example illustrates how to process a list of GeoLayers corresponding to counties:

  • The list of counties is specified as a property CountyList. Other commands can also be used to create a list.
  • The For command uses this property via its ListProperty="CountyList" parameter.
  • The For command IteratorProperty="County" parameter indicates which property will be used to iterate through the list items. The property value is set to the values in the list for each iteration.
  • Other commands can then use the syntax ${County} to dynamically fill filenames, etc. In this example the county name is used in GeoLayer filenames.
SetProperty(PropertyName="CountyList",PropertyType="str",PropertyValues="Adams,Washington,Jefferson")
For(Name="Counties",IteratorProperty="County",ListProperty="CountyList")
  # Process a file for each county
  ReadGeoLayerFromGeoJSON(InputFile="${County}-census.geojson",GeoLayerID=${County}-census-population")
EndFor(Name="Counties")

Troubleshooting

See Also