current community

your communities

more stack exchange communities

Stack Exchange
tour help
Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.
up vote 3 down vote favorite
2

How to remove or delete column fields in a shape file using python?

share|improve this question

2 Answers 2

up vote 4 down vote accepted

If you get no joy with QGSVectorLayer::deleteAttribute as they docs say: delete an attribute field (but does not commit it) have a look at the data provider. As QGIS deals with lots of feature types with different drivers I suspect that it's left up to the driver as to whether or not a field can be deleted.

Here's some code that I dredged up that may help:

fields = vlayer.dataProvider().fields()

count = 0
for name, field in fields.iteritems():
    if field.name() == fieldName:
        return count
    count += 1

To get the index of the field from the name. In this case I'm not using .upper() but I would recommend it.

After getting the index of the field you (might) delete it using the dataprovider.

fList = list()
fList.append(count)
vlayer.dataProvider().deleteAttributes(fList)

It's expecting a list so the integer needs to be put into a list. I have not used this method; normally I would use ArcMap to delete the field.

share|improve this answer
2  
vLayer.fieldNameIndex('YourFieldName') might be a easier way to get index –  vinayan Aug 1 '14 at 5:05
    
Thanks @vinayan, I have overlooked that one. The code I took this from is quite old, that function may be newer than my code. –  Michael Miles-Stimson Aug 1 '14 at 5:23
    
Thanks, It worked well Is there way to get max. index number ? I have an error "return outside function" Thanks for answers –  Nahm Aug 1 '14 at 23:47
    
Thanks for answers all of my problems solved and I combined ideas to find max. field index by following ways count = layer.dataProvider().attributeIndexes() print count maxindex = count[-1] print maxindex –  Nahm Aug 2 '14 at 0:34
up vote 3 down vote

There's several methods but I will mention the ones I normally use, both using the Python Console.

For SINGLE shapefiles:

  • Method 1 - Using a method utilising the QGIS algorithm - Delete Column:

    output_0=processing.runalg('qgis:deletecolumn', myshapefile.shp, "myFirstField", None)
output_1=processing.runalg('qgis:deletecolumn', output_0['OUTPUT'], "mySecondField", None)
output_2=processing.runalg('qgis:deletecolumn', output_1['OUTOUT'], "myThirdField", myoutput.shp)

  • Method 2 - Deleting the fields directly by selecting the layer from the Layers window (Table of Contents) and using the following code:

    layer = qgis.utils.iface.activeLayer()              # Sets the selected layer as the active layer
res = layer.dataProvider().deleteAttributes([0])    # The [0] represents the 1st field, so [1] is the 2nd field etc. To delete multiple fields, use the comma to separate. Eg. [0, 2, 4]
layer.updateFields()                                # Updates the layer with the changes

For MULTIPLE shapefiles:

  • Following on from Method 1, you can use the following script which was tested with 2 folders on the Desktop - "Testing" (which contained the shapefiles) and "Results" (which will contain the output shapefiles of the script):

    import processing, os, glob

from os.path import expanduser
home = expanduser("~")

result_path = home + "\Desktop\Results\\"
os.chdir(home + "\Desktop\Testing\\")

for fname in glob.glob("*.shp"):
    output_0=processing.runalg('qgis:deletecolumn', fname, "myFirstField", None)
    output_1=processing.runalg('qgis:deletecolumn', output_0['OUTPUT'], "mySecondField", None)
    output_2=processing.runalg('qgis:deletecolumn', output_1['OUTPUT'], "myThirdField", result_path + fname)

print "All done!"

  • Following on from Method 2, you can use the following code if you have multiple shapefiles loaded in your Layers window without having to select them individually. 

    for layer in QgsMapLayerRegistry.instance().mapLayers().values():
    res = layer.dataProvider().deleteAttributes([0])
    layer.updateFields()

Hope this helps!

share|improve this answer
    
I've done as you suggested in the 1st method but appeared this comment: "Error: Wrong parameter value: None". I can´t use the 2nd method because I have to do the same for a large number of shapefiles, about 8000. Any idea? –  Patrícia Fernandes Jun 30 at 13:16

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.