topic Re: Calculate repeating values in field in Python Questions

Calculate repeating values in field

JeffBaker2 — Fri, 13 Oct 2017 22:48:50 GMT

Anyone have any ideas how to calculate a field so the values (going down the table) are

etc. to the end of the table?

These values will end up being color codes for rendering. The actual values will be from 0-9, but need some way to get the repeating values in. Another option might be to calculate random values instead of repeating values. Any thoughts?

Re: Calculate repeating values in field

DanPatterson_Retired — Sun, 12 Dec 2021 07:17:24 GMT

cnt = 0
def seq_num_max(val):
    global cnt
    if cnt < val:
        cnt += 1
    else:
        cnt = 0
    return cnt

# in expression box ... seq_num_max(3) ... will number from 0 to 3 before repeating‍‍‍‍‍‍‍‍‍‍

will get you started ... for use in the field calculator obviously

Re: Calculate repeating values in field

MicahBabinski — Sun, 12 Dec 2021 07:17:26 GMT

I think this would do it:

In field calculator Codeblock (Python):

def Calculate(repeatingValue):
    interval = 1
    if cntr < 3:
        cntr += interval
    else:
        cntr = 1
    return cntr‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Then in your expression it would be Calculate(!YourFieldName!)

Micah

Re: Calculate repeating values in field

DarrenWiens2 — Sun, 12 Dec 2021 07:17:29 GMT

for i in range(10):
    print (i % 3) + 1

1
2
3
1
2
3
1
2
3
1‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Calculate repeating values in field

JeffBaker2 — Mon, 16 Oct 2017 14:59:44 GMT

Thanks for your replies. Dan, Micah, each of your code pieces seems to run well, but the values are not populating in the highlighted field. All rows remain Null--see below. Ideas?

Re: Calculate repeating values in field

MicahBabinski — Mon, 16 Oct 2017 15:03:30 GMT

Hey Jeff,

You'll need to apply that function in the main calc expression box:

seq_num_max(!ColorCode!)

That should do it.

Re: Calculate repeating values in field

JeffBaker2 — Mon, 16 Oct 2017 16:53:22 GMT

I am now getting all zero's in the ColorCode field. Am I setting up the Field Calculator dialog correctly? Or maybe something else?

Re: Calculate repeating values in field

JamesCrandall — Sun, 12 Dec 2021 07:17:32 GMT

import arcpy
import pandas

repeat_vals = [1, 2, 3]
df = pandas.DataFrame(range(100), columns=['col1'])
df = df.join(pandas.DataFrame(repeat_vals * (len(df)/len(repeat_vals)+1), columns=['col2']))
print df.values‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Calculate repeating values in field

JeffBaker2 — Sun, 12 Dec 2021 07:17:35 GMT

A little more info now . . .

Each time I run this code:

cnt = 0
def seq_num_max(val):
    global cnt
    if cnt < val:
        cnt += 1
    else:
        cnt = 0
    return cnt

The result calculates ALL values to 0, then to 1, then to 2, then 3, then back to 0 again, and so on. Still not sure how to get the repeating values?

Re: Calculate repeating values in field

DarrenWiens2 — Sun, 12 Dec 2021 07:17:37 GMT

This passes the current field value to the function (not what you want - would pass all 0s first time, then all 1s, etc.):

seq_num_max(!ColorCode!)‍‍

Try (you always want 3):

seq_num_max(3)‍‍‍

And code block (untested):

cnt = 0
def seq_num_max(val):
    global cnt
    if cnt < val:
        cnt += 1
    else:
        cnt = 0
    return cnt

Or (untested):

cnt = -1
def seq_num_max(val):
  global cnt
  cnt += 1
  return (cnt % val) + 1‍‍‍‍‍

Re: Calculate repeating values in field

JeffBaker2 — Mon, 16 Oct 2017 17:59:14 GMT

And Darren hits the grand slam . . . that worked! Thank you!

You gave two suggestions--the second one did the trick.

Thanks to all who shared your ideas.

Re: Calculate repeating values in field

DanPatterson_Retired — Mon, 16 Oct 2017 18:23:55 GMT

If you are running my code... then

seq_num_max(3) ... notice you put the number in not ColorCode... You are calculating ColorCode using ColorCode, not the maximum number that you want

Re: Calculate repeating values in field

JamesCrandall — Sun, 12 Dec 2021 07:17:40 GMT

As an alternative to the field calculator, this is a mix of libraries and ultimately simply uses a dictionary and arcpy.da.UpdateCursor to calculate the field with the repeating values.

(really, I had been looking for a reason to dive into using a dictionary to update with an UpdateCursor and this was a good exercise to nail that down).

import arcpy
import pandas
import numpy as np
import sys

#set the repeating values to use
repeat_arr = [1, 2, 3]

#the feature class to be updated, the field to calculat and a join field
fc = r'H:\DescribeFGDB\Readme.gdb\RptLyr'
updateField = 'calcIt'
idField = 'OBJECTID'

#convert the feature class to an array with OID values
nparr = arcpy.da.FeatureClassToNumPyArray(fc, ['OID@'])
#get array as pandas dataframe and populate the repeating values column
df = pandas.DataFrame(nparr)
df = df.join(pandas.DataFrame(repeat_arr * (len(df)/len(repeat_arr)+1), columns=['calcIt']))
#convert back to a numpyarry
x = np.array(np.rec.fromrecords(df.values))
names = df.dtypes.index.tolist()
x.dtype.names = tuple(names)

#convert to an in_memory table, set join field and the field to use to calculate with
arcpy.da.NumPyArrayToTable(x, r'in_memory\finalarr')
joinTab = r'in_memory\finalarr'
joinIdField = 'OBJECTID'
joinValueField = 'calcIt'

#create dictionary from the in_memory table
valueDic = dict ([(key, val) for key, val in arcpy.da.SearchCursor(joinTab, [joinIdField,joinValueField])])

#update the source feature class with the dictionary values, joining on the joinfields
with arcpy.da.UpdateCursor(fc, [updateField, idField]) as cursor:
    for update, key in cursor:
        if not key in valueDic:
            continue
        row = (valueDic [key], key)
        cursor.updateRow(row)

del cursor‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍