If I have a vector layer in QGIS, how do I use Python to find the maximum value which a given field has?

I need to convert the values in one field into values between 0 and 1. I guess I therefore need to set it to val/maxVal. That's why I need to find the maximum value.

  • and what if I'd like to evaluate the maximum for each unique value? This doesn't work at all...could someone find the error? thanks uniquevalues=layer.uniqueValues(index,limit=10000) for uv in uniquevalues: features = layer.getFeatures() for feat in features: values = [] attrs = feat.attributes() values.append(attrs[field]) if feat[field] == uv: maxarea = max(values)
    – FedericaZ
    May 17 '17 at 15:44

It is not necessary to get a complete list of field values. In QgsVectorLayer exists 'maximumValue' method. So, this works well and it's shorter:

layer = iface.activeLayer()

idx = layer.fieldNameIndex('fieldName')
print layer.maximumValue(idx)
  • 1
    I really should read the API more often ;)
    – Joseph
    Sep 15 '16 at 12:04
  • Perfect - just what I needed, and works perfectly. Thanks! Sep 15 '16 at 12:46
  • 3
    Just a note - the biggest advantage of using QgsVectorLayer.maximumValue over iterating through every value is that maximumValue can hand calculation of the maximum over to the data source itself. Ie, for a Postgres layer QGIS will send a simple "select max("field") from ..." query to the database, rather then having to fetch every single feature from the database and iterate through them. It's a dramatic performance win.
    – ndawson
    Sep 15 '16 at 22:07
  • Not working on string columns. Code proposed by Joseph fix te issue.
    – Kostadin
    Jan 16 '18 at 14:07

The accepted answer does not work in QGIS3.

Now one has to do:


(I am setting fieldname as the first line to make it easier to cut and paste for someone wanting to test it with their layer)


You could use the following in the Python Console to print out the maximum value for a given field:

values = []
layer = qgis.utils.iface.activeLayer()
idx = layer.fieldNameIndex('fieldName')
for feat in layer.getFeatures():
    attrs = feat.attributes()

print max(values)
  • 1
    It is not necessary to get a complete list of field values. In QgsVectorLayer exists 'maximumValue' method.
    – xunilk
    Sep 15 '16 at 12:02
  • 1
    Also works, but @xunilk's is the better solution. Sep 15 '16 at 12:47
  • @TomChadwin - Can't argue there =)
    – Joseph
    Sep 15 '16 at 12:49

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