QGIS - separate parcel attributes in attribute table with python

Question

I'd like to be able to split the parcel information in an attribute table from one column

parcel_value = 247/34

into two separated columns by using a PyScript

parcel_num = 247

and

parcel_den = 34

I was starting with this but then ran out of knowledge:

layer = iface.activeLayer()
for field in layer.fields():
 if field.name() == 'parcel_value':
 with edit(layer):
 idx = layer.fields().indexFromName(field.name())
 layer.renameAttribute(idx, 'parcel_num')

Answer 1

You can use the code snippet below. Instead of renaming and updating the "parcel_value" field, I would recommend adding two new integer fields, since after splitting the attribute values, you now have numeric data, and should store it as such.

layer = iface.activeLayer()
layer.dataProvider().addAttributes([QgsField('parcel_num', QVariant.Int), QgsField('parcel_den', QVariant.Int)])
layer.updateFields()
num_idx = layer.fields().lookupField('parcel_num')
den_idx = layer.fields().lookupField('parcel_den')
att_map = {}
for f in layer.getFeatures():
 if f['parcel_value'] != NULL:
 att_split = f['parcel_value'].split('/')
 num = att_split[0]
 den = NULL
 if len(att_split) == 2:
 if att_split[1]:
 den = att_split[1]
 att_map[f.id()] = {num_idx: num, den_idx: den}
 
layer.dataProvider().changeAttributeValues(att_map)
# Uncomment lines below to delete the original field (personally, I would leave it but it's up to you)
#layer.dataProvider().deleteAttributes([layer.fields().lookupField('parcel_value')])
#layer.updateFields()

Result:

enter image description here

• Matt: And if you want to change something later on, or something goes wrong, you still have your original data to work with :)
• Marek: @Ben W: i forgot to mention, that in some cases there is no denominator in the parcel_value column. In that case the value of the parcel_value should land in 'parcel_num'. without adressing that problem, the results are NULL. Otherwise it works perfectly.
• Ben W: @Marek, see my updated answer which will cover the case you describe.

Answer 2

If you have already set the column names of parcel_num and parcel_den in the attribute table, you can run the following code which will extract values before and after the forward slash / into separate columns. The code assumes the column types of the parcel_num and parcel_den are integers.

layer = iface.activeLayer()
with edit(layer):
 for feature in layer.getFeatures():
 value = feature['parcel_val'] # update the field name of the parcel_value 
 print(value)
 feature['parcel_num'] = value.split('/')[0]
 feature['parcel_den'] = value.split('/')[1]
 layer.updateFeature(feature)

Before running the code:

enter image description here

After running the code:

enter image description here

Without PyQGIS, you can also achieve the same results using Field Calculator:

• Check Update Existing Field and select parcel_num

• Write the following expression

   regexp_replace("parcel_val" ,'(\\d+)/(\\d+)','\1円')
  

Do the same steps for parcel_den

• Check Update Existing Field and select parcel_den

• Write the following expression

   regexp_replace("parcel_val" ,'(\\d+)/(\\d+)','\2円')
  

Where parcel_val is the name of the field that holds the parcel values, for example, 247/34.

You will get the same results as before.