topic Re: Calculate field conditional statement using a date formula in Python Questions

Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 06:25:26 GMT

Hi all,

I am using ArcGIS 10.3 to update a field with a numeric value that represents the elapsed time since the data was captured. I can do this in a python script that I have attached to a model but I also want to be able to sometimes do it quickly from within ArcGIS desktop and I am stumped.

I have written a 3 step process:

1. Create an integer field then calculate the number of days since today (field name = ET):

In Field Calculator, ET =

(datetime.datetime.now() - arcpy.time.ParseDateTimeString(!ActivityDate!)).days

2. Create a conditional Statement for "Elapsed Time" field as follows:

Expression:

Reclass(!ET!)

def Reclass(ET):

if ( ET < 28):

return 1

elif ( ET>= 28 and ET < 91):

return 2

elif ( ET >= 91 and ET < 182):

return 3

elif ( ET >= 182 and ET < 365):

return 4

elif (ET >= 365):

return 5

3. Delete the ET field

I really just want to declare a variable in my conditional statement for ET which would save having to create then delete the ET field, but everything I have tried does not work, for example:

Expression:

Reclass(ET)

ET = (datetime.datetime.now() - arcpy.time.ParseDateTimeString(!ActivityDate!)).days

def Reclass(ET):

if ( ET < 28):

return 1

etc etc

I cannot find any examples of conditional statements that use a variable instead of a field value in the Field Calculator, so any help would be appreciated.

Re: Calculate field conditional statement using a date formula

NeilAyres — Wed, 10 Feb 2016 06:39:53 GMT

And what errors are you getting?

Have you imported the datetime module?

Re: Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 06:55:37 GMT

The error says Error 000989: Python syntax error: Parsing error SyntaxError: invalid syntax (line 1).

I dont import the datetime module in Field Calculator.

The code for calculating the difference between today and and the collection day as an integer value works fine in Field calculator but its not happy when you try to create a variable using the same code.

Re: Calculate field conditional statement using a date formula

DanPatterson_Retired — Wed, 10 Feb 2016 09:08:15 GMT

you need to import datetime... just put it in front of the def line

Re: Calculate field conditional statement using a date formula

XanderBakker — Wed, 10 Feb 2016 11:25:07 GMT

... and if it is not the missing import statement, you may want to look at the content of the field !ActivityDate!. If the content is not valid and cannot be parsed to a datetime it will fail at arcpy.time.ParseDateTimeString(!ActivityDate!)

Re: Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 23:09:36 GMT

Unfortunately the import datetime does not work - I'm still getting the same error.

just to re-iterate, I am using arcGIS 10.3 desktop and am using the Calculate Field tool.

The code now looks like this (but doesn't work):

import datetime

ET = (datetime.datetime.now() - arcpy.time.ParseDateTimeString(!ActivityDate!)).days

def Reclass(ET):

if (ET < 28):

return 1

elif (ET >= 28 and ET < 91):

return 2

elif (ET >= 91 and ET < 182):

return 3

elif (ET >= 182 and ET < 365):

return 4

elif (ET >= 365):

return 5

!ActivityDate! content does contain valid date values and the code string

(datetime.datetime.now() - arcpy.time.ParseDateTimeString(!ActivityDate!)).days

works fine on its own, just wont work when I use it in this context.

Re: Calculate field conditional statement using a date formula

DanPatterson_Retired — Wed, 10 Feb 2016 23:20:19 GMT

ET should be inside the def, just after it

def Reclass(a_fld)

ET = blah blah blah ...TimeString( a_fld )

Reclass(!ActivityDate! ) should be in the timelapesed = box

You pass a field to the function

The function will contain a variable name, it shouldn't be the actual field name

your ET function should be within the def block not before

You should really parse the ET function into

nowww = (datetime.datetime.now() # before the code block

ET = (nowww - the reset of the original equation)

Re: Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 23:24:47 GMT

OK thanks will try that

Re: Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 23:41:02 GMT

OK thanks Dan! Below is what worked. (It didnt work if I parsed the ET function into nowww before the def block though).

Expression:

Reclass(!ActivityDate!)

import datetime

def Reclass(DateFld):

ET = (datetime.datetime.now() - arcpy.time.ParseDateTimeString(DateFld)).days

if (ET < 28):

return 1

elif (ET >= 28 and ET < 91):

return 2

elif (ET >= 91 and ET < 182):

return 3

elif (ET >= 182 and ET < 365):

return 4

elif (ET >= 365):

return 5

Re: Calculate field conditional statement using a date formula

MoyaCalvert — Wed, 10 Feb 2016 23:43:25 GMT

PS I just tried it without import datetime and it still works (which makes sense)

Re: Calculate field conditional statement using a date formula

DanPatterson_Retired — Sun, 12 Dec 2021 05:01:34 GMT

Moya ... et al...

For future reference

Using either numpy or the bisect module makes things much simpler when trying to do a sequential value reclassification ... whether it be text or numbers. Some thoughts and brief tests, before put into functions.

dts = [1,28,29,91,92,182,183,365,366]
bins = [28,91,182,365,400]

import numpy as np
c = np.digitize(dts, bins, right=True) + 1

result list(c) = [1, 1, 2, 2, 3, 3, 4, 4, 5]

import bisect   
d = [ bisect.bisect_left(bins,i) + 1  for i in dts]

results ditto

If these were put into a function they could do the reclassification for you.

In the examples here, a value of 1 was added to the returned indices to produce your new classification scheme.

The example #2 could be modified to turn it into a generator from a list comprehension.

I will post more on my blog when I get some more time and report back here. These nested, multilevel if, else if, adnauseum, else statements have to go .

Re: Calculate field conditional statement using a date formula

DanPatterson_Retired — Thu, 11 Feb 2016 11:47:17 GMT

The final link with code blocks using numpy and bisect modules

List comprehensions 3 ...

if - elif - elif - elif - else free examples