How do I populate an attribute field with the number of selected records?

TysonBarlow

I'm working with two datasets:
1) School Boundaries (polygons)
2) Students (points)


In the school boundary dataset I have fields for each grade (Grade1, Grade2, etc...) and would like to populate those fields with the number of students for each respective grade in each school boundary. The Students dataset has a field that contains each student's grade.

I have been doing it manually, but figure there should be a way to automate this process. Any help is appreciated, and if I haven't explained myself well enough, please let me know.

Thanks!

T__WayneWhitley

OK -- it's a new day...
I confess I made some silly mistakes on your script, Tyson, and toward the end of this thread, I simply wasn't testing enough before posting!  I've identified the critical error - not eliminating the 'P' values from the very beginning.  Of course, it may be more advisable to apply a def query (or use Make Feature Layer with a query) on the Students dataset to eliminate the 'P' values there - that way the subsequent spatial join processing doesn't deal with them whatsoever and outFields will not contain those vals.

I post this (below; also attached) for you to test yourself - I've included more comments this time within the script itself, no error trapping so use at your own risk.  I've assumed that whether Kindergarden or Preschool is determined only by the 1st letter, K or P, respectively.  That simplifies things just a little.  I tested it on both shapefile and feature class...the query filter for the cursor (at the beginning) was formed to eliminate blank or NULL values, so it will work whether using shapefile or feature class.

I would have coded the whole task including the spatial join and included error trapping, and even investigated further higher-performing or more concise Python techniques available to you (like the use of a dictionary), but I was sort of lazy and frankly the last part of the problem turned out to trip me up in small but rather befuddling ways - probably this sort of 'raw' approach is better for you anyway, to aid in understanding the whole process?

Enjoy, and let me know if you have any questions.

-Wayne

import arcpy  # Change these 2 input parameters accordingly... fc = r'E:\schoolTestData\test.gdb\schoolJoinToPolys' outField = 'outGrades'  delField = arcpy.AddFieldDelimiters(fc, outField)  # This query works whether shapefile or gdb fc. query = delField + ' IS NOT NULL AND ' + delField + ' NOT IN (\' \')'  rows = arcpy.UpdateCursor(fc, query)  for row in rows:      # This populates a list, row by row...      # outGradesRaw will potentially contain 'P' vals.      # outGrades is a new list with 'P' vals eliminated.      outGradesRaw = row.getValue(outField).split(',')      outGrades = []      for each in outGradesRaw:          if not each[0:1] == 'P':              outGrades.append(each)       # sorted outGrades for loop, comparison of successive items              outGrades.sort()       # initializing count      count = 0      compareVal = outGrades[0]       # Loop over the sorted list to count.      for each in outGrades:           if each == compareVal:                count += 1           else:                # This conditionally sets the fieldName to load...                if not compareVal[0:1] == 'K':                     fieldName = 'Grade_' + str(int(compareVal))                else:                     fieldName = 'Grade_K'                     # Successive K vals may not match,                     # so will be temp stored in att table,                     # then fetched to make a cumulative count.                     count += row.getValue(fieldName)                 # count committed to row obj from att table                row.setValue(fieldName, count)                # row obj committed to cursor obj of att table                rows.updateRow(row)                 # resetting count to 1                count = 1                 # setting compareVal to current val                compareVal = each                      # load the count for the last val, identical to part of above block      if not compareVal[0:1] == 'K':           fieldName = 'Grade_' + str(int(compareVal))      else:           fieldName = 'Grade_K'           count += row.getValue(fieldName)      row.setValue(fieldName, count)      rows.updateRow(row)  del rows

pySchool2.py.zip