Get next element of cursor arcpy

KyleDunaway1 — Tue, 23 May 2017 22:59:01 GMT

I am trying to compare two values, and can't seem to access the next row in a cursor.

for i, row in enumerate(cursor):

if row[0] == cursor.next()[0]

Any ideas?

Re: Get next element of cursor arcpy

RandyBurton — Wed, 24 May 2017 00:31:22 GMT

See this thread for ideas: Compare value from n and n+1 row in searchCursor

Re: Get next element of cursor arcpy

JoshuaBixby — Sun, 12 Dec 2021 03:44:39 GMT

Beyond reading through the thread recommended by Randy Burton‌, a couple of questions:

What type of cursor(s) are you working with?
What happens if the condition is satisfied?

UPDATE: continued....

As mentioned in the referenced GeoNet discussion, ArcPy cursors do not implement any kind of look- or read-ahead feature. If one is working solely within DBMSs, there are likely set-based approaches that are better then using cursors for look-ahead functionality, .e.,g LAG and LEAD functionality implemented in many DBMSs; but one needs to work with what is available to them.

There are multiple ways to emulate look- or read-ahead functionality with Python and ArcPy, several are covered in the aforementioned GeoNet discussion. Since I commented on that discussion last year, I have refined the approach I put forward. Functionally, the approach below is not any different, but syntactically it is much more streamlined, I would argue more Pythonic.

from itertools import izip_longest

fc =   # path to feature class
flds = # string list of field names for cursors

with arcpy.da.SearchCursor(fc, flds) as n1_cur:
    with arcpy.da.UpdateCursor(fc, flds) as n_cur:
        filler_row = next(n1_cur)
        for n_row, n1_row in izip_longest(n_cur, n1_cur, fillvalue=filler_row):
            if n_row[0] == n1_row[0]:
                n_cur.updateRow([...])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍
‍‍‍‍‍‍‍‍‍‍‍

The basic approach is to pair a search cursor with an update cursor. The search cursor is used for the look ahead (n+1 cursor or n1_cur) while the update cursor is used for the current record (n cursor or n_cur). The itertools.izip_longest() function is used to pair the two cursors so they can be stepped through together, with the search cursor being one record ahead of the update cursor.

UPDATE 2: Removed empty_row and created filler_row since previous code for empty_row would fail with datetime or geometry fields.

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