topic Re: Searchcursor Returns only First Field in Field_Name List in Python Questions

Searchcursor Returns only First Field in Field_Name List

BenjaminBarton — Sun, 12 Dec 2021 06:46:46 GMT

Greetings, I am running into a small problem. SearchCursor documentation states that search cursors can handle multiple field_names yet the below script only returns the first field name explicitly stated in the field_names parameter of the search cursor. If I use an asterisk, it returns the first field name in the list. I need it to return the location_id and lat and long attributes respectively from the view I am querying. Is it possible for a searchcursor to return more than one column / field?

#Explicitly defined object IDs known to be conflated in conflation data model
objectIDList = (55555,44444) #small test
#gets distinct location_ids
def getUniqueLocIDs():
tableRegistry = os.path.join(conn, "myView")
 fields = ['objectid', 'location_id', 'latitude', 'longitude']
whereExp = "objectid IN {0}".format(objectIDList)
 uniqueLocIDs = list(set("{0}".format(row[0]) for row in arcpy.da.SearchCursor(tableRegistry, ['location_id', 'latitude'], whereExp)))
return list(uniqueLocIDs)
print(getUniqueLocIDs())‍‍‍‍‍‍‍‍‍‍

Re: Searchcursor Returns only First Field in Field_Name List

PavanYadav — Sun, 12 Dec 2021 06:46:49 GMT

See if the following helps:

uniqueLocIDs = list(set("{0}, {1}, {2}".format(row[0], row[1], row[2]) 
    for row in arcpy.da.SearchCursor(tableRegistry, 
        ['location_id', 'latitude'], whereExp)))‍‍‍

Re: Searchcursor Returns only First Field in Field_Name List

DanPatterson_Retired — Sun, 12 Dec 2021 06:46:51 GMT

your where expression is fine

objectIDList = (55555,44444)
whereExp = "objectid IN {0}".format(objectIDList)
whereExp
'objectid IN (55555, 44444)'‍‍‍‍

but why are you only including 2 fields instead of using your 'fields' list

arcpy.da.SearchCursor(tableRegistry, ['location_id', 'latitude'], whereExp) current

arcpy.da.SearchCursor(tableRegistry, fields, whereExp) maybe?

Re: Searchcursor Returns only First Field in Field_Name List

RandyBurton — Sun, 12 Dec 2021 06:46:54 GMT

I like using dictionaries:

sourceFC = "somefeature"

sourceFieldsList = [ 'location_id', 'latitude', 'longitude' ]
whereExp = "objectid IN {0}".format(objectIDList)

uniqueLocIDs = {r[0]:(r[1:]) for r in arcpy.da.SearchCursor(sourceFC, sourceFieldsList, where_clause=whereExp)}

# { location_id: ( latitude, longitude), .... )‍‍‍‍‍‍‍‍

Re: Searchcursor Returns only First Field in Field_Name List

JoshuaBixby — Thu, 28 Feb 2019 16:29:44 GMT

This code will generate an IndexError because the tuple being returned from the search cursor only has 2 items.

Re: Searchcursor Returns only First Field in Field_Name List

JoshuaBixby — Thu, 28 Feb 2019 16:36:35 GMT

Your problem lies in Line #8. Instead of troubleshooting the line as written, what are you trying to achieve with that line? You are creating a list from a set, so it appears you are looking for a list of unique items, correct? If so, what defines uniqueness, location_id, latitude, or both?

Re: Searchcursor Returns only First Field in Field_Name List

BenjaminBarton — Thu, 28 Feb 2019 16:49:19 GMT

End state is to retrieve location_id, lat and long by passing in a list of objectIDs but there exists a 1:M rel between location_ids and object ids (one location id can match to multiple objectIDs) in this non-normalized view I am querying. My result needs to be normalized so while I am using object id to match on to resolve distinct location_id keys, I don't necessarily need objectID in my result set. This leads me to believe that maybe I need to retrieve the normalized key structure as first pass to establish the normalized relational framework or key structure which the block of code I provided does do when just passing object_id in as the field param, and then query for my attributes using that returned key or keys in a second pass with another search cursor, but before I get to that point, I just wanted to figure out why only one column in fields() returns, regardless of whether I provide an explicit list, use an asterisk (all) or pass in 'fields' as the param. It just returns the first column of whatever is passed in as a param regardless of which method I use.

Re: Searchcursor Returns only First Field in Field_Name List

JoshuaBixby — Thu, 28 Feb 2019 17:00:59 GMT

I only have time at the moment to address:

I just wanted to figure out why only one column in fields() returns, regardless of whether I provide an explicit list, use an asterisk (all) or pass in 'fields' as the param.

Your answer is:

"{0}".format(row[0])‍

The search cursor is returning everything you are asking, you are ignoring everything but the first column.

Re: Searchcursor Returns only First Field in Field_Name List

BenjaminBarton — Sun, 12 Dec 2021 06:46:57 GMT

This did the trick. My apologies for only having latitude explicitly specified as as one of the field parameters. it should have been:

(tableRegistry, ['location_id', 'latitude', 'longitude'], whereExp)‍‍‍‍‍‍‍‍

And here is the final:

Returns exactly what I wanted it to without having to do a second pass with a separate search cursor to pull in the attributes. For context, there are two object IDs (non-normalized) that match on a conflated location_id I am returning (object IDs below are anonymized) but I only want one location_id (normalized) and the associated set of lat long coords returned:

objectIDList = (55555,44444) #small test
#gets distinct location_ids
def getUniqueLocIDs():
tableRegistry = os.path.join(conn_hg, "plc.plc.conflated_places_lv1")
 fields = ('objectid', 'location_id', 'latitude', 'longitude')
whereExp = "objectid IN {0}".format(objectIDList)
 uniqueLocIDs = list(set("{0}, {1}, {2}" .format(row[0], row[1], row[2]) for row in arcpy.da.SearchCursor(tableRegistry, ['location_id', 'latitude', 'longitude'], whereExp)))
return list(uniqueLocIDs)
#getUniqueLocIDs()
print(getUniqueLocIDs())‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Searchcursor Returns only First Field in Field_Name List

DanPatterson_Retired — Sun, 12 Dec 2021 06:46:59 GMT

format parsing doesn't care what goes in as long as it is one object. If you have more 'objects', then they would need to be separated by commas

"stuff {}".format([1,2,3,4])
Out[6]: 'stuff [1, 2, 3, 4]'

"stuff {}".format([1,2,3,4][0])
Out[7]: 'stuff 1'

"stuff {}".format([1,2,3,4][1:])
Out[8]: 'stuff [2, 3, 4]'

"stuff {}".format([[1,2,3,4], [5,6,7,8]])
Out[9]: 'stuff [[1, 2, 3, 4], [5, 6, 7, 8]]'‍‍‍‍‍‍‍‍‍‍‍