[GIS] Edit Field Value of Feature Class Using Python in ArcGIS 10.2

arcgis-10.2arcgis-desktopattribute-tablepython

I have a feature class whose attribute table looks like this:

Latitude | Longitude | Area

For the area column, all rows are null. I would like to put in a specific value for all rows using Python.

I know how to do this on the front-end in the ArcMaps application ( right click > Open Attribute Table > right click on column > field calculator > input value).

How can I accomplish this programmatically using Python?

Best Answer

You can calculate the values for a column with Python by using either a GP tool Calculate Field or arcpy UpdateCursor (this one is faster when working with large datasets).

For calculating the geometrical properties of features, you can either use GP tool Add Geometry Attributes or using tokens (such as SHAPE@AREA) of update cursor.

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[GIS] How to Populate new field using expression containing MAX value from another field in ArcGIS attribute table using field calculator

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)

[GIS] Create Feature Class From XY Table Using Python

You make no mention that you have any problems reading your text file, so I am assuming that it is just how to get the coordinates into a feature class that has you stumped.

There are a number of ways to do this so some suggestions to start looking at are:

NumPyArrayToFeatureClass (arcpy.da) (with ExtendTable (arcpy.da)]2 for the attributes)
InsertCursor (arcpy.da)

Both have code examples that I think should get you past where you are stuck. I recommend getting the code samples to work first and then try to apply to your situation second.

Best Answer

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[GIS] How to Populate new field using expression containing MAX value from another field in ArcGIS attribute table using field calculator

[GIS] Create Feature Class From XY Table Using Python

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