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I have a line feature class representing road segments, with each road segment having a unique ID. This feature class has an attribute of average observed daily traffic counts. I have another table which contains more information about each road segment, but each road segment ID in the table has 8 entries (each of which corresponds to a 3-hour period).

I've set up a Relate between the feature class and the table, and have added a new field to the feature class that I would like to populate with the sum of 8 values from the table that share the same road segment ID (i.e. one attribute, represented by 8 measurements from different times-of-day).

I'd like to do this using the Field Calculator or Model Builder. Python would be preferred over VBScript.

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  • Might you be interested in using python and not doing this in the field-calculator?
    – djq
    Commented Dec 15, 2011 at 17:56
  • @celenius I'm most interested in finding a way to do this purely through the ArcGIS UI. I had considered writing a standalone Python script that would essentially iterate through each ID in the table and output the summed values to a new table, which would be fairly simple, but I am hoping to find a short code snippet that allows for this to be done in the Field Calculator -- or possibly even a ModelBuilder method -- that doesn't require the creation of a new table.
    – nmpeterson
    Commented Dec 15, 2011 at 18:03
  • Yes - I was thinking of the same approach that you describe for a standalone script. I haven't figured out how to examine sections of the attribute table from within the UI; I await answers with interest!
    – djq
    Commented Dec 15, 2011 at 18:09

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While this isn't a Field Calculator method, have you considered creating a Database View of 3hr table? You could summarize the 8 entries per RoadID, then create a simple Join data back to the road featureclass, rather than using the relate.

If you are using a RDBMS, you could make a dynamic View through it's internal methods that you could simply Join to the road featureclass. This would keep the tabular summary data always up-to-date.

If you need to do this in a pGDB or fGDB, you could script the process through ModelBuilder fairly easily, although you would need to update the data manually. And by using the "in_memory" workspace, you would also avoid creating a temporary table on disk.

The process I would use would be something like: Input Table-> Summarize data-> Make View (in_memory)-> Join field to shapefile.

Tools you would likely use include:

  • Summary Statistics
  • Make Table View
  • Join Field (ArcInfo) or Add Join (ArcView/Editor)

Read up in the ArcGIS online help for specifics of each tool.

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  • Great solution! Summary Statistics is a nifty tool :)
    – nmpeterson
    Commented Dec 15, 2011 at 19:00
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    The only caveat I would mention here is if versioning is involved. If so, creating a view from the DBMS side on a versioned table will cause the view to look at the "base" table and not include later revisions. A multiversioned view can be used in that case, though there is a performance hit for using it.
    – Michael Todd
    Commented Dec 15, 2011 at 19:37
  • @Michael, very good point! Thanks for adding your experience to this answer.
    – RyanKDalton
    Commented Dec 15, 2011 at 20:58

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