How to read the attribute values using pyqgis?

How to read the attribute values using pyqgis?

Once you have a QgsFeature object you can use the attributes () method to retrieve the attributes (a.k.a. columns or fields) associated with that feature (a.k.a. row), e.g.: If you want to index the field by it’s name, rather than a number, you need to use the field mappings:

How to add a field to a QGIS map?

Add the layer into QGIS map canvas and open the attribute table. Can be seen as in figure 1 the new field Length and the length values has been added to each feature. Figure 1.

How to create a QGIS layer in Python?

1 layer = iface.activeLayer (): This line uses the iface object and runs the activeLayer () method which returns the currently selected layer in QGIS. 2 layer.startEditing (): This is equivalent to putting the layer in the editing mode. 3 layer.deleteAttribute (1): The deleteAttribute () is a method from QgsVectorLayer class.

How to get the attributes in a table?

In order to get the information in a table you would first have to access the layer’s features. In my case I put the features in a variable. Then you loop through the features, and for each feature you call its attributes, which can then be printed using their column index .

How to add a vector layer in QGIS?

This QGIS Python Tutorial series will discuss about how to get features of a vector layer, add or delete a field and updating attribute value. I think this tutorial is quite interesting because in the previous post already discussed how to add a vector layer into QGIS map canvas.

How to delete a field in QGIS Python?

To delete a field, simply can be used deleteAttributes method from data provider class. The method required a list that contains field index to be deleted. For example we want to delete the Length field that already added before which has index 4. When done, don’t forget to call updateFields method to make the change take in place.

How to get list of layer names using pyqgis?

I need a list containing the names of all the layers in a QGIS session. I did the task as but this has the problem that only the names for the visible layers are extracted.

How to make a cheat sheet for pyqgis?

Cheat sheet for PyQGIS — QGIS Documentation documentation The code snippets on this page need the following imports if you’re outside the pyqgis console: 20. Cheat sheet for PyQGIS ¶ 20.1. User Interface ¶ 20.2. Settings ¶ 20.3. Toolbars ¶ 20.4. Menus ¶ 20.5. Canvas ¶ 20.6. Layers ¶

How to add a field in QGIS Python?

After that using addAttributes method then a field is added using QgsField class with taken two parameters: Field Name and Type. For field’s type can be defined using QVariant.

How to access the features of a layer in QGIS?

When the layer is open in QGIS, the selected features are highlighted. The layer method selectAll () allows for selecting all features in a layer and removeSelection () can be used to clear the selection.

How to iterate over selected features in pyqgis?

Iterate over a selection Once we have selected features, we may want to perform operations for only the selected features. This can be accomplished by iterating through only the layers that are selected. We can return the selected features with layer.selectedFeatures (), then iterate through those features.

How to select all features in a layer?

It is very simple to select all features in a layer. We simply use the code layer.selectAll (). Selecting by ID selects a feature based on the feature id, of FID. The FID is a unique identifier for each feature in a layer. Generally, the FID corresponds to the order in which features were created.

What can you do with a QGIS console?

QGIS brings a Python API (see PyQGIS Developer Cookbook for some code sample) to let the user interact with its objects (layers, feature or interface). QGIS also has a Python console.

How to execute code snippets in pyqgis cookbook?

Open PyQGIS Cookbook by typing _pyqgis. You can execute code snippets from the output panel by selecting some text and pressing Ctrl+E. No matter if selected text contains the interpreter prompt ( >>>, ). Use the Show editor button to enable the editor widget.

How to calculate field values in QGIS Python?

This is where calculating field values with the QGIS Python API (PyQGIS) can really help you out. With the PyQGIS API you can easily automate any operation you could do in the QGIS field calculator. To calculate field values with PyQGIS all you need to do is set up an expression and apply that expression to the attribute table of your vector file.

How do I save a layer in pyqgis?

First, we save all layers with a specified name to a variable. Then open the first layer in that list as a QgsVectorLayer. Next, we need to save the layer capabilities. This will tell us what actions we can and can’t take with the this layer.

How to add fields to a feature layer?

As out turns out, there were problems in the script. First, as @artwork21 pointed out, layer.updateFields () needed to be added update the fields in the layer. In addition, the fields also needed to be set in the features within the layer.

How to show only selected features in a QGIS attribute table?

Just drag a box around the features you want to select and the features’ outline will change to indicate the selection. Open the QGIS attribute table by right-clicking on the layer in the table of contents. Select ‘Open Attribute Table’ from the list that appears. Now the attribute table will open.

Where to find city population data in QGIS?

The data about city population are contained in the attribute “pop_max”, as you can see if you select the Identify tool and click on any of the points to examine the available attributes: Use this method if your layer is not already loaded in QGIS.

How to print all field names in pyqgis?

To print all field names to the console, we can use a for loop: You can read these two lines of code as: For each field in the vector layer’s fields, print the field name. In this case, fields () is a function of our vector layer object while field is a variable name that can be chosen freely.

Can you copy without vector geometries in QGIS?

You can copy the information without vector geometries if you deactivate the Copy geometry in WKT representation from attribute table option in Settings ‣ Options ‣ Data Sources menu. QGIS provides two view modes to easily manipulate data in the attribute table:

How to copy attribute data from QGIS to excel?

If you want to use attribute data in external programs (such as Excel, LibreOffice, QGIS or a custom web application), select one or more row (s) and use the Copy selected rows to clipboard button or press Ctrl+C. In Settings ‣ Options ‣ Data Sources menu you can define the format to paste to with Copy features as dropdown list:

How do you perform table joins in QGIS?

Create the table join. Table joins in QGIS are performed using QgsVectorJoinInfo object. We need to specify the GEO.id2 field from the CSV layer as the Join Field and the GEOID field from the shapefile layer as the Target Field. Once you run the following code, the shapefile layer will have additional attributes joined from the csv layer.

Do you have to load both layers in qgsvectorjoininfo?

A common pitfall when using QgsVectorJoinInfo is that both the layers must be loaded in the QgsMapLayerRegistry – otherwise the join would not work. An easier – and preferred way of accomplishing the same thing is via the Processing Framework.

How to load zipped layers in QGIS using Python?

Loading zipped layers in QGIS via Python. Using QgsGraduatedSymbolRendererV2 to apply a graduated style to a vector layer. Download the following files to your computer. You can type the following commands in the Python Console or the built-in Editor in QGIS. Load the shapefile. The Census Tracts file is a zip file containing the shapefile.

How can I add a Vector attribute table to print composer?

It is possible to add parts of a vector attribute table to the Print Composer canvas: Click the Add attribute table icon, click and drag with the left mouse button on the Print Composer canvas to place and size the item. You can better position and customize its appearance in the Item Properties panel.

Where to find the attribute table item in QGIS?

Current atlas feature (see figure_composer_table_atlas ): you won’t see any option to choose the layer, and the table item will only show a row with the attributes from the current feature of the atlas coverage layer. and Relation children (see figure_composer_table_relation ): an option with the relation names will show up.

How to print attributes for all fields in QGIS?

To print attributes for all fields, simply omitted the index. Now let’s play a little bit with a conditional term, for example we just want to know which park that has area more than 200 Ha. For this we make a loop to check each feature with has area more than 200 Ha and count the number. …….

Do you need to access feature geometry in pyqgis?

Copying, or updating the shape or location of a feature requires you to access the feature’s geometry. This tutorial will show the basics of accessing feature geometry with PyQGIS. This example uses a line feature, but can be easily adapted for lines or polygons.

Where is the conditional formatting panel in QGIS?

You can enable the conditional formatting panel clicking on at the top right of the attributes window in table view (not available in form view). The new panel allows user to add new rules to format rendering of Field or Full row . Adding new rule opens a form to define: font.

What do you need to know about pyqgis development?

Raster Layers 3.3. QgsProject instance 4. Accessing the Table Of Contents (TOC) 4.1. The QgsProject class 4.2. QgsLayerTreeGroup class 5. Using Raster Layers 5.1. Layer Details 5.2. Renderer 5.3. Query Values 6. Using Vector Layers 6.1. Retrieving information about attributes 6.2. Iterating over Vector Layer 6.3. Selecting features 6.4.

How to create a vector layer in pyqgis?

Selecting features 6.4. Modifying Vector Layers 6.5. Using Spatial Index 6.6. The QgsVectorLayerUtils class 6.7. Creating Vector Layers

How to start a QGIS project in Python?

Python Plugins 1.3. Running Python code when QGIS starts 1.4. Python Applications 1.5. Technical notes on PyQt and SIP 2. Loading Projects 2.1. Resolving bad paths 3. Loading Layers 3.1. Vector Layers 3.2. Raster Layers 3.3. QgsProject instance 4. Accessing the Table Of Contents (TOC) 4.1. The QgsProject class 4.2. QgsLayerTreeGroup class 5.

How to create a new field in Python?

I attach a small example following the idea you want to make. But if you do it without any union field you will overwrite values.

How to open the attribute table in attributtabelle?

To open the attribute table for a vector layer, activate the layer by clicking on it in the Layers Panel. Then, from the main Layer menu, choose Open Attribute Table. It is also possible to right-click on the layer and choose Open Attribute Table from the drop-down menu, or to click on the Open Attribute Table button in the Attributes toolbar.

How to open the attribute table in a regular window?

According to the setting in Settings ‣ Options ‣ Data sources menu, the attribute table will open in a docked window or a regular window. The total number of features in the layer and the number of currently selected/filtered features are shown in the attribute table title, as well as if the layer is spatially limited.

How to create a vector layer in QGIS?

In the code editor, or console, create a variable containing the path to your vector file. Now we’ll simultaneously assign the vector layer to the layer variable and load it into the QGIS interface. This adds the layer into the QGIS interface.

How to select features from a vector layer?

This adds the layer into the QGIS interface. In the legend, the vecotr is labeled with the file name. There are multiple ways to select features from a shapefile (or other vector file). In this tutorial, we will cover selecting all features, selection by ID and selection by attribute values.

How to list unique values in attribute table?

Lists unique values of an attribute table field and counts their number. Parameters¶ Inputlayer[vector: any] Layer to analyze. Targetfield[tablefield: any] Field to analyze. Outputs¶ Uniquevalues[html] Analysis results in HTML format.

How to create a list of unique values in QGIS?

Console usage¶ processing.runalg(‘qgis:listuniquevalues’,input_layer,field_name,output) See also¶ next previous| QGIS User Guide» Processing providers and algorithms» QGIS algorithm provider» Vector table» If not stated otherwise, all content is licensed under Creative Commons Attribution-ShareAlike 3.0 licence (CC BY-SA)

How to get field names in pyqgis 2.0?

I am trying to change an plugin from QGIS 1.8 to 2.0. In the 1.8 version I create a table of the field names like this:

How does the vector Layer constructor work in QGIS?

The vector layer constructor in turn instantiates a QgsVectorDataProvider subclass corresponding to the provider type, and passes it the url. The data provider connects to the data source.

How to create new field based on other vector layers?

I’d like to create a new field in vector layer “Join”, based on attributes in vector layers “Buildings” and “Intersection” but PyQgis returns a series of worng numbers, particularly just the first feature value of the field “Intersection” (I suppose the error is in the for cycle’s script/sequence). Could you help me?

How to run a QGIS processing algorithm in Python?

You can also run a QGIS Processing algorithm via Python using the processing.runAndLoadResults () function instead of processing.run () as shown above – which will load the result to QGIS canvas directly.

Is it possible to filter based on attributes in QGIS?

Starting with QGIS 2.10 it is even possible that filtering in such a way will give you some extra performance over other types of filtering (like python implementations). You are using a layer with the postgis provider At the moment (2.16) many more than just postgis provider implement this (spatialite, ogr, oracle…).

How to use expressions in a pyqgis script?

Open the attribute table and you’ll see that the last three fields are empty. Let’s fill them with expressions! The expression syntax is exactly the same as in the field calculator GUI. So you can test them in the GIU first, before copying them into your PyQGIS script. The first expression computes the revenue per employee.

How to add global and project scopes in pyqgis?

(QgsExpressionContextUtils.globalProjectLayerScopes () is a convenience function that adds the global, project, and layer scopes all at once. Alternatively, those scopes can also be added manually. In any case, it is important to always go from “most generic” to “most specific” scope, i.e. from global to project to layer.) Now we’re ready!

How to add feature in shape file with pyqgis?

If you want to add a new layer, the call for it is like the one below (the keyword is Polygon). The first and last points will be the extremities, while the middle ones will provide the actual shape (curvature) of the line feature

How to select features from a layer in QGIS?

Select features from a layer using expressions. Deselect features from a layer using the Attributes toolbar. Using Query Builder to show a subset of features from a layer. Natural Earth has a nice Populated Places dataset. Download the simple (less columns) dataset For convenience, you may directly download a copy of datasets from the link below:

How to find all unique attributes in QGIS?

If you aren’t sure about the field values, you can click the Load all unique values to see what the attribute values are present in the dataset. For this exercise, we are looking to find all features that have a population greater than 1,000,000. So complete the expression as below and click Select.