Assign quartile value to records in a field

EmekaUde

Hello, I am quite new to running complex codes for field calculation tasks. 

I have a field with a number of records. I want to create another field and calculate what quartile class each record falls under say 25th, 50th, 75th or 100th. 

So basically I need help to calculate and determine the quartile class of each records in a particular field.

Thank  you for your help

 

Hornbydd

You can complete this task with some python scripting which you can run directly within ArcPro from the python console.

Here is an example table of my input layer, 12 rows with the values I want to put into quartile classes in the field Value and QClass is the field to record which class they are in, note the rows are all NULL as the code has yet to be run.:

 

The code you drop into the python console is this, you just need to change the layername and fields in the search and update cursors to match your data.:

 

import arcpy, numpy
layername = "testdata" # Name of layer as seen in TOC
lstValues = list()     # list to store values in

# Read values into list
with arcpy.da.SearchCursor(layername, "Value") as cursor:
    for row in cursor:
        lstValues.append(row[0])

# Use numpy to compute quartiles
q25 = numpy.percentile(lstValues, 25)
q50 = numpy.percentile(lstValues, 50)
q75 = numpy.percentile(lstValues, 75)
print("Q25 = " + str(q25))
print("Q50 = " + str(q50))
print("Q75 = " + str(q75))

# Write quartile class back to layer
with arcpy.da.UpdateCursor(layername, ["Value","QClass"]) as cursor:
    for row in cursor:
        v = row[0] # The value
        if v < q25:
            row[1] = 25
        elif v >= q25 and v < q50:
            row[1] = 50
        elif v >= q50 and v < q75:
            row[1] = 75
        else:
            row[1] = 100
        cursor.updateRow(row)

Print("Finished!")

 

 

The results are shown, sorted by QClass: