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I have a vector layer in QGIS with various numeric fields and I would like to calculate the percentiles, 90-95-99, for each of the fields. I have tried the GRASS v.univariate algorithm but this only does one percentile at a time. Any suggestions?

Grant Boxer
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  • Where do you want these percentiles? If you sort on a feature, then the 90th percentile value will be the value of the attribute for the feature at row 0.9 times the number of features. You could simply read that off - I'm not sure how to get a whole set of attribute values into an array to do it in an expression. Otherwise you might need a python function. – Spacedman Mar 06 '21 at 08:43

1 Answers1

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You can use pyqgis with numpy.percentile:

import numpy as np

#Change these two lines to match your data:
lyr = QgsProject.instance().mapLayersByName('ok_my_riks')[0]
fieldname = 'area'


data =[f[fieldname] for f in lyr.getFeatures()] #List all values in column


for p in [90, 95, 99]:
    print("{0} th percentile is: {1}".format(p, np.percentile(data, p)))

enter image description here

BERA
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