Deleting field in shapefile based on values in field using ArcPy

Question

I'm trying to create a Python script to automate simplifying some feature classes (shapefiles). The data table for my shapefiles look like this (all of the fields except the first four are SHORT):

FID    Shape*    GEOID10            EMS_ORI    A_CO01    A_CO05    A_CO06    A_CO11
___________________________________________________________________________________
0      Polygon   421110218001027    E56001     99        23        99        17
1      Polygon   421110218001231    E56001     99        24        30        15
2      Polygon   421110218001028    E56001     99        24        99        16
3      Polygon   421110218001035    E56001     99        24        99        99

and so on. I am trying to find an easy way to delete an entire field if it only contains the value "99" for every row. In this example, I would want to delete the A_CO01 field because all features in this shape file have a value of 99 there. I do not want to delete A_CO06 or A_CO11, because at least one feature has a value other than 99 in each of those fields. My shapefiles have thousands of features, so I tried to script this with Python in an instant Python window in ArcCatalog. I'm only a novice at Python, so I know I'm missing something easy, but here's what I tried:

import arcpy

fc = 'E:/EMS500_Polygons.shp'
fields = arcpy.ListFields(fc)

for field in fields:
    if (field.name == "FID" or field.name == "Shape" or field.name == "GEOID10" or field.name == "EMS_ORI"):
        continue
    else:
        if (field.type = "Integer" and min(field) == 99):
            arcpy.DeleteField_management(fc, field)

This gives me a syntax error on line 10: if (field.type = "Integer" and min(field) == 99):. What I'm trying to do is delete any field where the MIN value of the entire field is 99 (this value is a "placeholder"; valid values for this field range from 1 to 93).

Answer 1

min(field) will not work and should give you some error like

TypeError: 'Field' object is not iterable

Try:

import arcpy
fc = r"C:\folder\shapefile.shp"
fields = arcpy.ListFields(fc)

#Find minimum value per numeric field and store in a dictionary: "fieldname:minval"
numeric_fields = [field.name for field in fields if any(ftype in field.type.lower() for ftype in ['double', 'int'])]
values = [row for row in arcpy.da.SearchCursor(fc,numeric_fields)] #List all values for the numeric fields
mindict = {}
mindict.update({fld:val for (fld,val) in zip(numeric_fields, min(values, key=lambda x: min(y for y in x if y is not None)))})

for field in fields:
    if (field.name == "OBJECTID" or field.name == "Shape" or field.name == "GEOID10" or field.name == "EMS_ORI"):
        continue
    else:
        if 'int' in field.type.lower() and mindict[field.name] == 99:
            print(field.name)
            arcpy.DeleteField_management(fc, field.name)

To avoid listing shape and object id fields you can try using .required method:

if somefieldname not in [f.name for f in arcpy.ListFields(fc) if f.required]

Answer 2

Okay, I figured it out using your example. I changed the last line to arcpy.DeleteField_management(fc, field.name) and that worked.

Here is the complete working code:

import arcpy
fc = r"E:/Shapefile.shp"
fields = arcpy.ListFields(fc)
fieldList = []

#Find minimum value per numeric field and store in a dictionary: "fieldname:minval"
numeric_fields = [field.name for field in fields if any(ftype in field.type.lower() for ftype in ['double', 'int'])]
values = [row for row in arcpy.da.SearchCursor(fc,numeric_fields)] #List all values for the numeric fields
mindict = {}
mindict.update({fld:val for (fld,val) in zip(numeric_fields, min(values, key=lambda x: min(y for y in x if y is not None)))})

for field in fields:
    if (field.name == "OBJECTID" or field.name == "Shape" or field.name == "GEOID10" or field.name == "EMS_ORI"):
        continue
    else:
        if 'int' in field.type.lower() and mindict[field.name] == 99:
            print(field.name)
            arcpy.DeleteField_management(fc, field.name)