Python code help for ArcGIS Field Calculator tool (Model Builder)

Question

Is there any python code that:

1st, sort a column (example name by alphabet)

2nd, grab the first cell of sorted column and assigned it to a variable like A=..

I need all of this to be done in field calculator and inside show block. Please give me a sample or help.

Answer 1

You'll want to use the data access search cursor (requires ArcGIS 10.1+) for this task, and its sql clause functionality. The sql clause allows for sorting.

Here's the python code that assigns the first non-null value in the sorted field to the varaible var:

#Path to feature class
fc = r"C:\Path\To.gdb\Feature Class" 
#Field name
fld = "Field_Name"

sqlClause = (None, "ORDER BY {0} ASC".format (fld))

with arcpy.da.SearchCursor (fc, fld, sql_clause = sqlClause) as cursor:
    for val, in cursor:
        if val:
            break
del cursor

example:

I recommend doing this outside of the field calculator, and instead as a python script imported into ModelBuilder, so that each row calculated doesn't create a new cursor.

Answer 2

Given all what I've seen so far it seems to me the best approach is to use the Calculate Value tool in ModelBuilder.

Expression:

getval(r"%featureclass%", "FIELDNAME")

Code Block:

import arcpy
def getval(fc, fld):
    # get the first non-null field value
    where = "{} IS NOT NULL".format(fld)
    val = arcpy.da.SearchCursor(fc, fld, where).next()[0]
    return val

Data Type:

 Any value

Answer 3

instead of sorting,

1. do a select by attribute > [field] is not NULL.
2. then on the selected table 'collect a value' it will naturally take the value in the first row of your field since all the Nulls are selected out that should be fine.
3. Then do a select attribute again and choose 'CLEAR SELECTION' to make sure the rest of your analysis doesn't happen on a subset of your data. Make the 2nd step a precondition of the 3rd step so that the selection is not cleared before the value is collected.