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Mastering  QGIS

You're reading from   Mastering QGIS Go beyond the basics and unleash the full power of QGIS with practical, step-by-step examples

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Product type Paperback
Published in Sep 2016
Publisher Packt
ISBN-13 9781786460370
Length 486 pages
Edition 2nd Edition
Tools
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Authors (5):
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John Van Hoesen, GISP John Van Hoesen, GISP
Author Profile Icon John Van Hoesen, GISP
John Van Hoesen, GISP
Kurt Menke, GISP Kurt Menke, GISP
Author Profile Icon Kurt Menke, GISP
Kurt Menke, GISP
Paolo Corti Paolo Corti
Author Profile Icon Paolo Corti
Paolo Corti
Richard Smith Jr., GISP Richard Smith Jr., GISP
Author Profile Icon Richard Smith Jr., GISP
Richard Smith Jr., GISP
Luigi Pirelli Luigi Pirelli
Author Profile Icon Luigi Pirelli
Luigi Pirelli
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Toc

Table of Contents (13) Chapters Close

Preface 1. A Refreshing Look at QGIS FREE CHAPTER 2. Creating Spatial Databases 3. Styling Raster and Vector Data 4. Preparing Vector Data for Processing 5. Preparing Raster Data for Processing 6. Advanced Data Creation and Editing 7. Advanced Data Visualization 8. The Processing Toolbox 9. Automating Workflows with the Graphical Modeler 10. Creating QGIS Plugins with PyQGIS and Problem Solving 11. PyQGIS Scripting Index

Iterating over features

Now, it's time to discover how to get all the features or a subset of them. The main way to iterate over all features or records of myVector is by using the following code, which shows the ID of each feature:

for feature in myVector.getFeatures():
  feature.id()

This will print a list of all the 653 record IDs as shown here:

0L
1L
...[cut]...
652L

It's not always necessary to parse all records to get a subset of them. In this case, we have to set the QgsFeatureRequest class parameters to instruct getFeatures and then retrieve only a subset of records; in some cases, we must also retrieve a subset of columns.

The following code will get a subset of features and columns:

rect = QgsRectangle(  1223070.695,  2293653.357 , 9046974.211,  4184988.662)

myVector.setSubsetString(' "AREA_MI" > 1000 ')
request =  QgsFeatureRequest()
request.setSubsetOfAttributes([0, 2])
request.setFilterRect( rect )

for index, feature in enumerate( myVector.getFeatures...
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