topic Re: Field Calculator: Generate Random Numbers failure in Python Questions

Field Calculator: Generate Random Numbers failure

RichardThurau — Fri, 25 Feb 2011 14:08:52 GMT

Hello,
I'm new to python so hopefully the solution is simple.

I am trying to generate random integers between 1 and 1000 to populate the field "Rand2".
The "Rand2" field is Float.

####
Pre-Logic Script Code:

import arcpy

# Set the randomGenerator environment to 4 MERSENNE_TWISTER
arcpy.env.randomGenerator = "4 MERSENNE_TWISTER"

# Calculate a random number using the arcgis.rand() function
result = arcpy.CalculateValue_management("arcgis.rand('INTEGER 1, 1000')")

# Get the value from the result object from CalculateValue and print
randomValue = float(result.getOutput(0))
print randomValue

Expression:
Rand2=

randomValue[!Rand2!]
####

Field calculator runs for a while then delivers an "Error running expression" message (See image for full message).

Can anyone tell me how to clean this up?

Thanks

Rich

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Fri, 25 Feb 2011 15:21:38 GMT

if getoutput returns a list, then this line
randomValue = float(result.getOutput(0))

should be

randomValue = float(result.getOutput[0])

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Fri, 25 Feb 2011 17:04:24 GMT

Thanks Dan,

I made the change. But, still not functioning. Now error message is:

<type 'exceptions.TypeError'>: 'instancemethod' object is unscriptable.

Progress?

not sure

Rich

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Fri, 25 Feb 2011 17:55:44 GMT

so it isn't returning a python list, however, looking at the help files and your example I noted

'INTEGER 1, 1000' was your case
and in the help files at
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001w0000000w000000.htm
it was
'normal 0.0 10.0'
the only difference between them, excluding the distribution type, was that you had a pesky "," after the 1 in yours and the help files seems to suggest that a space delimited string is used. Barring that, try the help file example to rule out further issues.

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Fri, 25 Feb 2011 18:11:21 GMT

Yes, I've been trying all sorts of variations based on that example and what I can read about the function. From what I can see in the error messages, commas and capitalizations don't seem to matter too much.

I did try the tool originally using the provided script exactly as presented.

Either the documentation is wrong for arcgis.rand(), the documentation is leaving out some vital steps, I'm doing something wrong that no one has pointed out, or arcpy is screwed up on my machine.

Still trying though.

RT

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Fri, 25 Feb 2011 19:03:10 GMT

instead of
randomValue[!Rand2!]
try
randomValue(!Rand2!)

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Fri, 25 Feb 2011 19:17:53 GMT

You are a trooper Dan.

That was one of the first things I noticed between the code example in help, and the code examples that I saw others post.

I just tried it again anyway, with not success. I even got rid of defining the distribution. Current code block is:

import arcpy

# Calculate a random number using the arcgis.rand() function
result = arcpy.CalculateValue_management("arcgis.rand('normal 0.0 10.0')")

# Get the value from the result object from CalculateValue and print
val = float(result.getOutput[0])
print val

Expression is:
val(!Rand2!)

I had to move on, so I generated a random table of values on Random.org's website, pasted into excel, joined the excel file, and used field calculator to copy the random values. That's a lot of work for what should be a simple code.

Of course I wouldn't spend so much time if I didn't think this was going to helpful to me in the future.

Therefore, i would greatly appreciate any attempts to find a fix.

Thanks a lot.

Rich

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Fri, 25 Feb 2011 19:28:11 GMT

Rich
I will look into it some more, try the code block that uses numpy's random in the interim

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Sat, 11 Dec 2021 17:39:29 GMT

stupids finally over

parser: Python

Code block

import numpy
def rand_num(a_field):
  return  numpy.random.randint(1,1000)

the rest

rand_num(!randnum!)
where !randnum! is the field to place the random numbers. I think you were mixing up the script example with the field calculator example and I just didn't catch it

or better still provide a minimum and maximum value

import numpy
def rand_num(min_val, max_val):
  return  numpy.random.randint(min_val,max_val)

with
rand_num(1,1000)

calling the function

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Sat, 26 Feb 2011 14:23:44 GMT

Well, this isn't very clear to me. I tried both examples you've given here. At least in a way I am interpreting. ArcGIS doesn't want to calculate either of them.

Like I said, I'm really new to using python, and I haven't successfully gotten anything to run from Filed Calculator yet.

I guess the question is, does this code work on your machine? I'm starting to think there could be something wrong with python or something on my machine.

I've attached an image of the code I'm trying to populate my Rand2 field with.

RT

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Sat, 26 Feb 2011 19:38:48 GMT

did you try the second as well? is your field an integer field? worked on my computer

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Sun, 27 Feb 2011 16:30:41 GMT

Dan,
Thanks so much for keeping it up.

Well, looks like my error is data specific. I don't know why yet, but that code will not run on the dataset I've been trying to generate random numbers for. However, it did run perfectly on another shapefile (that has far fewer features?).

It ran on a Long field (I had been trying both Long and Float).

At least now I know that numpy at least works on my machine.

There used to be a way to mark issues as solved on these forums, but I'm not seeing that option right now.

Thanks for your help!

Rich

Re: Field Calculator: Generate Random Numbers failure

DanPatterson_Retired — Sun, 27 Feb 2011 17:42:53 GMT

Just a check if it is that particular shapefile...

1 File|Data Export Data give it a new name and saving location
2 try the code on the "clone"

or if you have some bad records

3 select the first couple of records in the table and try running the code on the selection
4 if that still doesn't work, select one record, export to a new file and try again.

if that doesn't work...no clue

Re: Field Calculator: Generate Random Numbers failure

RichardThurau — Mon, 28 Feb 2011 13:20:45 GMT

Dan,
I've messed around with a few things. The code runs on some datasets but not others (does not run on an exported copy of original). Neither file name length, nor the number of records seems to matter. It ran on some polygon shapefiles but not others.

The key for me was just to figure this code out because it's a tool I will be able to use in the future. Hopefully, when that time comes, I'll either have a dataset with which the code works, or I'll figure out why it doesn't.

But, till then, I'm moving on.

Thanks again for your help. I was going a little nuts there for a bit.

Rich

Re: Field Calculator: Generate Random Numbers failure

deleted-user-ugCMpXci8bn5 — Sat, 11 Dec 2021 17:39:32 GMT

If you are still looking at this, I had luck with a slight variation of the code block given above:

(code block)

def rand_num():
  import random
  return random.randint(1,100)

then

(yourField) = rand_num()

Re: Field Calculator: Generate Random Numbers failure

JeffWard — Tue, 28 Apr 2015 20:04:11 GMT

For posterity, if you are hitting a data specific error, you can throw some debugging code in the script to see which records are giving you problems. In this case, you could pass in the ObjectID to the field calculator function and put it in and arcpy.AddMessage note. This way you would see how far things get before hitting the error.