topic Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1] in Python Questions

updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Mon, 08 Feb 2021 20:18:29 GMT

FileGDB
ArcGIS 10.4

Need to calculate elapsedSeconds column by first sorting on location_timestamp and then evaluate if PEP_land_name matches in row[n] and row[n+1]. If true, then set row[n+1] to elapsedSeconds value.

fields = ['PEP_land_name','location_timestamp','elapsedSeconds'] with arcpy.da.UpdateCursor(tracksToProcMonth, fields, sql, sql_clause=(None, 'ORDER BY location_timesatmp ASC')) as u_cur: with arcpy.da.SearchCursor(tracksToProcMonth,fields, sql, sql_clause=(None, 'ORDER BY location_timestamp ASC')) as cursor: for row in cursor: firstlLand = row[0] firstTimestamp = row[1] try: nextLand = cursor.next()[0] nextTimestamp = cursor.next()[1] if firstlLand == nextLand: tdt = nextTimestamp - firstTimestamp totSecs = tdt.total_seconds() print 'totSecs: {}'.format(totSecs) u_row = totSecs u_cur.updateRow() else: totSecs = 0.00 u_row = totSecs u_cur.updateRow()

I seem to be close in that I can arrive at the correct sort and evaluation, but I'm not exactly sure what to do about the updateCursor and setting the elapsedSeconds value in row[n+1]. In the attached image, OID 1 elapsedSeconds would be 0, OID 5 would be 5, and so on and on...

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

Anonymous User — Mon, 08 Feb 2021 20:52:25 GMT

u_cur.updateRow(row) Might be what you are after?

... You can move it out from the if/else conditionals because you are setting u_row either way.

if firstlLand == nextLand: tdt = nextTimestamp - firstTimestamp totSecs = tdt.total_seconds() print 'totSecs: {}'.format(totSecs) u_row = totSecs else: totSecs = 0.00 u_row = totSecs u_cur.updateRow(u_row)

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Mon, 08 Feb 2021 21:00:16 GMT

if the rows oid=1 and oid=5 (see image in op) are the 2 rows being evaluated and elapsedSeconds calculated, does your suggestion update row OID=5?

In the image OID=1 should be 0.00 seconds and OID=5 should be 5.00 seconds

Thanks!

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

Anonymous User — Mon, 08 Feb 2021 21:25:52 GMT

The first thing I saw from your code sample was u_row missing from the .updateRow(). I can't really answer your question without running it through the debugger and verifying that the rest of your code is valid. I can say that it will update whichever row 'u_row' is currently on.

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Mon, 08 Feb 2021 21:35:49 GMT

right... I think that's my problem: I cannot update row[n+1] rather than the current row.

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

Anonymous User — Mon, 08 Feb 2021 21:54:12 GMT

You could probably work the values into a dictionary and do the processing outside of the cursors and then come back to update the values by OID. I can work up a sample latter today if that is feasible.

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Mon, 08 Feb 2021 22:16:06 GMT

I'm also incorrectly implementing cursor.next()

It seems each time that is invoked it immediately skips to the next row. I'm not exactly sure how best to get the values for row n and n+1 WHILE the current row is at n.

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

DavidPike — Mon, 08 Feb 2021 23:20:26 GMT

Unless I've misinterpreted what you're trying to achieve, I think it can be done without and .next() or nested cursors.

I've just created global variables to hold the previous land and timestamp values for each row:

import arcpy fc = r'PathtoMyFC' previous_timestamp = '' previous_land = '' with arcpy.da.UpdateCursor(fc, ['landname', 'timestamp', 'elapsed']) as cursor: for row in cursor: this_timestamp = row[1] current_land = row[0] if previous_timestamp is not None and current_land == previous_land: time_diff = this_timestamp - previous_timestamp total_seconds = time_diff.total_seconds() row[2] = total_seconds previous_timestamp = this_timestamp previous_land = current_land cursor.updateRow(row)

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Mon, 08 Feb 2021 22:50:58 GMT

very promising.

...and simple. Love that.

Let me give it a go and check back but def looks preferable to nested cursors.

Thanks,

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JamesCrandall — Tue, 09 Feb 2021 00:44:18 GMT

I will go ahead and mark as the solution because it appears to work as intended and I am running into another issue that needs resolved in order to actually implement this.

Thanks again!

Re: updateCursor row[n+1] from searchCursor row[n]-row[n+1]

JoshuaBixby — Tue, 09 Feb 2021 16:27:01 GMT

From a semantics perspective, this is a n-1 solution and not n+1. It is not possible to do an n+1 with a single cursor or a single loop through a cursor.