3

This is my scenario:

  • List of names in a python list: a[]
  • A 1000 records shapefile with a column: 'name' (populated)
  • A second column called 'value'
  • ArcGIS environment (arcpy)

I want to update the column 'value' (i.e from 0 to 1) for all the shapefile records having a value in the column 'name' matching any of the list.

In terms of efficiency, I don't know which one is the best option:

A) Iterate through the list first; for each value of the list I start running through the shapefile asking for a match and do the update. Example: for 3 names; 3,000 reading operations on the shapefile.

B) Iterate through the shapefile first; for each record of the shapefile I look for a match on the list by iterating through the list each time. Example: for 3 names; 1,000 reading operations on the shapefile.

C) Use a dictionary instead, no list. Iterate through the shapefile first, and for each record, ask the dictionary for a value, if any, and do the update. Example: for 3 names; 1,000 reading operations on the shapefile.

4

If you have your values in a python list already, you only need to iterate through your shapefile. You can check if a value is in a list with if <value> in <list>:.

Example:

#full path to shapefile
shp = "C:\example\exampe.shp"

#check field
nameFld = "name"
#update field
valueFld = "value"
#update value
updateValue = 1

checkList = [...] #your values to check

import arcpy

#iterate rows in table
with arcpy.da.UpdateCursor (shp, [nameFld, valueFld]) as cursor:
    for name, value in cursor:
        #skip row if name value isn't in list
        if not name in checkList:
            continue

        #update
        row = (name, updateValue)
        cursor.updateRow (row)
  • Great use of a continue statement, +1 from me, shouldn't the #update be row[1]=updateValue? What happens to any other fields in the row if you set the row to the 2-value tuple? OP, name in checkList is case sensitive so beware of that situation and perhaps pre-process the checkList to all lower or upper case. – Michael Stimson Sep 24 '15 at 23:12
  • 1
    @MichaelMiles-Stimson da.UpdateCursor only changes input fields. Two fields in, so my two-object tuple will update the two indicated fields, and all others will remain as they are. – Emil Brundage Sep 24 '15 at 23:15

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