I've got one field X with 10 numerical attributes (float/double).
I've created a new field Y (also float/double) which I need to populate with the percentage of each record/attribute (in each of the 10 rows) relative to the MAX value in field X, i.e. something like Y=X/max(!X!).
I need to do this using the field calculator - in VB script or Python.
Any suggestions? I thought using max before the field name would suffice? (I assumed it was a built-in-function from Python in ArcGIS).
You cannot use the field calculator to find the maximum value within all of the rows in a field. However, the field calculator can perform operations horizontally, among rows using functions like max([!field1!, !field2!, !field3!]).
The only way to accomplish this is by using cursors outside of the field calculator. Try the following workflow:
Use a generator to list all of the row values in X and find the list max
maximum = max(row[0] for row in arcpy.da.SearchCursor(fc, ['X']))
Then loop through each row and perform the calculations:
with arcpy.da.UpdateCursor(fc, ['X','Y']) as cursor:
for row in cursor:
row[1] = row[0] / maximum
--
import arcpy
fc = r'C:\path\to\your\featureclass'
maximum = max(row[0] for row in arcpy.da.SearchCursor(fc, ['X']))
with arcpy.da.UpdateCursor(fc, ['X','Y']) as cursor:
for row in cursor:
row[1] = row[0] / maximum
cursor.updateRow(row)
I found a solution using arcpy.da.TableToNumPyArray in the Field calculator using Python. It first creates an Array (list) of all the 'X' values. Afterwards the max value is calculated and given a seperate variable. Last step is to divide this maxium value from each 'Y' value ('Scores', in my example below).
def my_rank(score_value):
my_list = arcpy.da.TableToNumPyArray ("Rank_test", "Scores")
my_max = my_list["Scores"].max()
ranking_score = score_value / my_max
return ranking_score
If there is no other more direct way you could create an empty list and populate it with x field, maximum in a list is then easily found and used to populate the y fields.
