Loop an operation in all features

Question

I have a layer that has date and time information and I need the difference between this information in seconds, I managed to get close to this but I needed to loop for the difference between the features. I used something like:

campotempo = pr.fieldNameIndex('Data/Hora GPS')
tempo1= feature1.attributes()[campotempo]
tempo2 = feature2.attributes()[campotempo]
tempo1form = datetime.datetime.strptime(tempo1, "%d/%m/%Y %H:%M:%S")
tempo2form = datetime.datetime.strptime(tempo2, "%d/%m/%Y %H:%M:%S")
datarange = ((tempo1form - tempo2form).seconds)
with edit(vl):
  for f in vl.getFeatures():
    f['Tempo(s)'] = datarange
    vl.updateFeature(f)

But it did not work

How can I use PyQGIS to make the difference between the time of each feature?

Answer 1

You can use an expression like this, which you can execute using python like this.

If you dont want to use expression you can:

import datetime
layer = QgsProject.instance().mapLayersByName("pointswithtime")[0]
timefield = "gpstime"

#Add the tempo field
pr = layer.dataProvider()
fieldname = "tempo"
pr.addAttributes([QgsField(fieldname, QVariant.Int)])
layer.updateFields()
ix = layer.fields().indexFromName(fieldname)
    
#List all features and sort by timestamp. You might want to sort by something else?
features = [[f.id(), datetime.datetime.strptime(f[timefield], "%d/%m/%Y %H:%M:%S")] for f in layer.getFeatures()]
features.sort(key=lambda x: x[1])

ids = [x[0] for x in features] #Extract the ids
timestamps = [x[1] for x in features] #And timestamps

#Calculate diff between row2-row1, row3-row2, ... and insert a starting None/NULL value
deltas = [None]+[(b-a).seconds for a,b in zip(timestamps, timestamps[1:])]

attributemap = {id : {ix: d} for id, d in zip(ids, deltas)} #A dict of {feature id : {fieldindex to update: value}, ..
pr.changeAttributeValues(attributemap) #Update the values

Answer 2

Check your field data type. If it is decimal you will have to convert your datarange variable to a float. Your code should work. I tested with putting a decimal in datarange. Also getting the difference between 2 datetimes should result in a datetime.timedelta.

    #Lists Fields in current layer
from datetime import timedelta
current_fields = []
layer = iface.activeLayer()
lfields = layer.fields()
for fld in lfields:
    fname = fld.name()
    current_fields.append(fname)
print(current_fields)
#datarange = timedelta(seconds = 4.5)
datarange = 4.5
with edit(layer):
  for f in layer.getFeatures():
    f['Tempo(s)'] = datarange
    f["Name"] = "hello"
    layer.updateFeature(f)