Is there a way to use python to select features by location from selected features?

Question

Hi, I have a script that seems to work but is unfortunately returning incorrect results. I am trying to figure out the best way to go about it. I have tried several other alternatives but those alternatives either return an incorrect number of results or doesn't have the data I need to work with. What I am trying to do is: * simply iterate through a set of features that have like fields * iterate through each null value in the fields, selecting another layer based on location to that null record in the feature class field * derive a certain field value from the feature that is selected based on the location of the feature class with null field value import arcpy import os arcpy.env.overwriteOutput = True workspace = r'Database Connections\......sde' fcs = [] walk = arcpy.da.Walk(workspace, datatype="FeatureClass") #make district landlot layer Dist_LL = "Database Connections\.....sde\......Landlots" DistLL_layer = arcpy.MakeFeatureLayer_management(Dist_LL, 'DLL_layer') for dirpath, dirnames, filenames in walk: for filename in filenames: fcs.append(os.path.join(dirpath, filename)) for fc in fcs: geometryType = arcpy.Describe(fc).shapeType #Get feature class name fcsname = os.path.basename(fc) name = os.path.splitext(fcsname) y = name[1].lstrip('.') print y #Create lists (OID) OID = [] if geometryType == 'Point': print geometryType for row in arcpy.da.SearchCursor(fc, ["OID@", "LANDDISTRICT", "LANDLOT"], """LANDDISTRICT IS NULL OR LANDLOT IS NULL"""): appendOID = OID.append(row[0]) OIDstrnum = str(len(OID)) #Create unique naming conventions a = '{}{}'.format(y, OIDstrnum) if (row[1] is None or row[2] is None): #Create temp fc copy b = arcpy.MakeFeatureLayer_management(fc, a) #Select layer by location selection = arcpy.SelectLayerByLocation_management(DistLL_layer, "INTERSECT", b, '', "NEW_SELECTION") print '{} District is {} and Land Lot is {} '.format(row[0], row[1], row[2]) for selected in arcpy.da.SearchCursor(selection, ["LAND_DIST", "LAND_LOT"]): print selected break elif (row[1] is None): print '{} Land District is {} '.format(row[0], row[1]) for selected_Lot in arcpy.da.SearchCursor(selection, ["LAND_DIST"]): print selected_Lot break elif (row[2] is None): print '{} Land Lot is {}'.format(row[0], row[2]) for selected_District in arcpy.da.SearchCursor(selection, ["LAND_LOT"]): print selected_District break else: print 'No null values' del OID[:]‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ I have something that works(partially) but does not return the correct features with a corresponding spatial location. If anyone could assist with this I would greatly appreciate it. Robert

RPGIS · Answer

Thanks Joshua,

I checked out the article and it makes complete sense to use a dictionary for this instance. The only thing is is that I have never used or created a dictionary before. It seems like it is a list almost but I am completely unfamiliar with this. If you or anyone gets a chance, could you possibly show me what that would look like specifically. The other thing that I am trying to obtain a single value that is derived for each value in a given instance. If there is a way to achieve this I would be very interested.

Thanks,

Robert

JoshuaBixby · Answer

Some quick comments. Your if/elif structure look better. From a functional perspective, you don't have to have parentheses around all the checks. For example, you could write: if row[1] is None and row[2] is None: Whether that is cleaner or easier to understand depends on the individual, but I just wanted to point it out. In general, you do not want to construct feature layers and cursors within a cursor loop. Having nested cursors is a performance killer, and constructing lots of feature layers within a cursor loop tends to create memory management issues if the data set is large. I recommend reading /blogs/richard_fairhurst/2014/11/08/turbo-charging-data-manipulation-with-python-cursors-and-dictionaries?sr=search&searchId=22a74f0f-d654-4aba-92b8-4249ddcaa4b1&searchIndex=1‌. It will give you some ideas for how you can using Python dictionaries to cut down or cut out nested cursors.

RPGIS · Answer

Hi Joshua, Here is the updated script. Issue 1: I came some of the features that may be corrupted and so being able to identify those and deleting them is something I am still trying to figure out. Issue 2: I am not sure how to set up the if/else statements in such a way that the three conditions can be identified. import arcpy import os arcpy.env.overwriteOutput = True workspace = r'Database Connections\....sde' fcs = [] walk = arcpy.da.Walk(workspace, datatype="FeatureClass") #make district landlot layer Dist_LL = "Database Connections\....sde\.....fc" arcpy.MakeFeatureLayer_management(Dist_LL, "DLL_layer") for dirpath, dirnames, filenames in walk: for filename in filenames: fcs.append(os.path.join(dirpath, filename)) for fc in fcs: geometryType = arcpy.Describe(fc).shapeType #Get feature class name fcsname = os.path.basename(fc) name = os.path.splitext(fcsname) y = name[1].lstrip('.') print y #Create lists (OID) OID = [] if geometryType == 'Point': print geometryType with arcpy.da.SearchCursor(fc, ["OID@", "LANDDISTRICT", "LANDLOT"], """LANDDISTRICT IS NULL OR LANDLOT IS NULL""") as selected_fc: for row in selected_fc: print row #Create temp fc layer arcpy.MakeFeatureLayer_management(fc, "fcLayer") #Select layer by attribute arcpy.SelectLayerByAttribute_management ("fcLayer", "NEW_SELECTION", "OBJECTID = {}".format(row[0])) #Select layer by location arcpy.SelectLayerByLocation_management("DLL_layer", "INTERSECT", "fcLayer", '', "NEW_SELECTION") if (row[1] is None) and (row[2] is None): print '{} District is {} and Land Lot is {} '.format(row[0], row[1], row[2]) for selectrows in arcpy.da.SearchCursor("DLL_layer", ["OID@", "LAND_DIST", "LAND_LOT"]): if selectrows is None: print selectrows elif (row[1] is None) and (row[2] is not None): print '{} Land District is {} '.format(row[0], row[1]) for selected_Lot in arcpy.da.SearchCursor("DLL_layer", ["OID@", "LAND_DIST"]): print '{} Land District = {}'.format(row[0], row[1]) elif (row[1] is not None) and (row[2] is None): print '{} Land Lot is {}'.format(row[0], row[2]) for selected_District in arcpy.da.SearchCursor("DLL_layer", ["OID@", "LAND_LOT"]): print '{} Land Lot = {}'.format(row[0], row[1]) else: print 'No null values' del OID[:]‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ The script works but I think there are areas where I could easily simplify this script. Any help on simplifying/identifying the best ways to resolve my issues would be greatly appreciated. Thanks, Robert