topic Re: How to write python expression and code block for Geometric Mean in Python Questions

How to write python expression and code block for Geometric Mean

ParthBansal — Tue, 09 Oct 2018 07:48:14 GMT

I am building a model to calculate geometric mean for each shape file in model builder. How to do write Expression and Code Block which would:

Take in shapefile "City_1" and use all the values in Field "Area" and calculate n√a*b*c*d. ..... where n are number of values in field "Area" and a,b,c,d are all the value in field "Area"

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Sun, 12 Dec 2021 07:35:00 GMT

an old one

https://community.esri.com/message/434687?commentID=434687#comment-434687

and it isn't done in the field calculator

fc = r"C:\GIS\A_Tools_scripts\aprx_info\aprx_info.gdb\SamplingGrids"
a = arcpy.da.TableToNumPyArray(fc, "Shape_Area")
a = a.view('float')
N = len(a)
loga = np.log10(a)
_sum = np.cumsum(loga)
gm = 10.0**((_sum[-1])/N)


# ---- results

a
array([1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000., 1000000., 1000000., 1000000., 1000000., 1000000.,
       1000000., 1000000.])

N  # ---- number of polygons from a fishnet
100

gm  # ---- geometric mean
1000000.0‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Sun, 12 Dec 2021 07:35:02 GMT

But as a code piece

fc = 'C:\\GIS\\A_Tools_scripts\\aprx_info\\aprx_info.gdb\\SamplingGrids'

def gm(fc):
    import scipy.stats as st
    a = arcpy.da.TableToNumPyArray(fc, "Shape_Area")
    a = a.view('float')
    return st.gmean(a)


# --- now feed it the featureclass or fc table

gm(fc)
999999.9999999978‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to write python expression and code block for Geometric Mean

XanderBakker — Tue, 09 Oct 2018 12:00:51 GMT

Or just use the standard tool Mean Center—Help | ArcGIS Desktop

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Tue, 09 Oct 2018 13:40:31 GMT

Xander Bakker do you suspect that the OP meant "geographic center" and not the geometric mean as in the mathematical definition? They are two different measures

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Sun, 12 Dec 2021 07:35:05 GMT

Since 'area' was mentioned... consider 3 land parcels of 10, 100, and 1000 hectares.

what is the mean-ish thing?

import scipy.stats as st

areas = np.array([10, 100, 1000])

st.gmean(areas)  # --- floating point 'issues' but 100
99.99999999999996


np.mean(areas)   # ---- hmmmmm ;)
370.0‍‍‍‍‍‍‍‍‍‍

Re: How to write python expression and code block for Geometric Mean

XanderBakker — Tue, 09 Oct 2018 18:08:20 GMT

A very good question Dan_Patterson , we'll see what the OP will respond, but your suggestions so far have been very helpful.

Re: How to write python expression and code block for Geometric Mean

ParthBansal — Wed, 10 Oct 2018 04:21:12 GMT

I meant geometric mean as in statistical value. Thanks!

Re: How to write python expression and code block for Geometric Mean

ParthBansal — Wed, 10 Oct 2018 04:28:10 GMT

Thank you. And when I said 'expression and code block' I was thinking about using 'calculate value' in model builder.

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Wed, 10 Oct 2018 09:35:03 GMT

the first example is a code block (def gm(a) ), just substitute your field name in the expression call …. gm(!YourFieldName!) … using a python parser.

The last one can be turned into a code block

import scipy.stats as st

def gm(a):

"""scipy version"""

areas = st.gmean(areas)

return areas

gm(!YourFieldName!)

This is the link to Calculate values to show you where to put stuff

Calculate Value—Tools | ArcGIS Desktop

Re: How to write python expression and code block for Geometric Mean

DanPatterson_Retired — Fri, 26 Oct 2018 00:44:37 GMT

I will mark as 'Assumed Answered' since you didn't close the thread