topic Re: Calculate Field Sum for Unique Set in Python Questions

Calculate Field Sum for Unique Set

JohnDye — Tue, 11 Jun 2013 20:03:39 GMT

I have a table that I've modified coming out of the Network Analyst OD Cost Matrix (If you've read my other post on getting a result object to a GDB Table, I am currently getting this out of ArcMap as a workaround).

The table looks something like this like this, where the latter three fields are type 'Double'

OriginID	DestID	Total_Length	MarketShare	Sum_MarketShare
112358924132	61124	1.24	24	55
112358924133	61124	1.36	26	44
112358924134	61124	1.54	32	64
112358924135	61124	1.72	54	109
112358924132	53856	1.36	21	55
112358924133	53856	.24	18	44
112358924134	53856	1.53	32	64
112358924135	53856	1.27	55	109

I need to calculate the 'Sum_MarketShare' field to determine the Sum off all market share for each unique Block Group set.

Re: Calculate Field Sum for Unique Set

DarrenWiens2 — Tue, 11 Jun 2013 21:03:32 GMT

If I understand correctly, you want to SUM the field MarketShare, grouped by some field (what is the Block Group?).

Two ideas:
1.) This is commonly done with the Summary Statistics tool (statistic=SUM, case_field=the Block Group field). Then, join (Add Join or Join Field) the result to the original table. Calculate the value into SUM_MarketShare. This can be done with Python or tools.
2.) Use cursors (SearchCursor and UpdateCursor) to sort, then loop through adding, then loop through updating, your data. This is Python only.

Not sure which takes longer to run. If you're doing this once, I'd use the tools. If not, spend time figuring out the cursors.

Re: Calculate Field Sum for Unique Set

RichardFairhurst — Tue, 11 Jun 2013 22:20:14 GMT

If I understand correctly, you want to SUM the field MarketShare, grouped by some field (what is the Block Group?).

Two ideas:
1.) This is commonly done with the Summary Statistics tool (statistic=SUM, case_field=the Block Group field). Then, join (Add Join or Join Field) the result to the original table. Calculate the value into SUM_MarketShare. This can be done with Python or tools.
2.) Use cursors (SearchCursor and UpdateCursor) to sort, then loop through adding, then loop through updating, your data. This is Python only.

Not sure which takes longer to run. If you're doing this once, I'd use the tools. If not, spend time figuring out the cursors.

Paired cursors in any form always take longer than Summary Statistics and Field Calculator in my experience. Those two tools are far more optimized than the Python or ArcObjects cursors.

Re: Calculate Field Sum for Unique Set

JohnDye — Wed, 12 Jun 2013 18:35:25 GMT

This is commonly done with the Summary Statistics tool

Darren,
That's exactly what I was looking for! Thanks!!

Re: Calculate Field Sum for Unique Set

JohnDye — Wed, 12 Jun 2013 18:37:01 GMT

This is commonly done with the Summary Statistics tool

Darren,
That's exactly what I was looking for! 700+ tools makes it hard to find something when you don't know the name! Thanks!!