deleting selected features (footprint shapes)

Question

hi !

[ usually I am the person giving answers .. on CityEngine .. 🙂 ]

though I am new to Python coding in ArcGIS, so I'd be happy if anyone could help me with the following issue :

I have a layer with a few hundred shapes, where I am creating manual selections. based on those selected features, I'd like to delete n% of the selected shapes. e.g. 10% each time I run the script to 'thin out' the data in certain regions.

any input welcome .. !

MatthiasBuehler1 · Answer

hi Chris !

thanks for that input ! appreciated.

I'll have a look at this.

matt

ChrisSnyder · Answer

This code should give you a random 10% sample of the OBJECTIDs in a feature layer that have a selected set.#Warning: Untested
import random, arcpy
samplePct = 0.1
arcpy.MakeFeatureLayer_managment(roadsFC, "roads", "")
arcpy.SelectLayerByAttribute_managment("roads", "NEW_SELECTION", "ROAD_TYPE = 'Highway')
fidSetList = [int(fid) for fid in arcpy.Describe("roads").fidSet.split(";")]
if len(fidSetList) * samplePct >= 1: #error check rto make sure you have enough selected features to get an appropriate sample
   randomSampleList = radom.sample(fidSetList, int(len(fidSetList) *samplePct))
else:
   print "Not enough selected features to constitute a " + str(samplePct * 100) +  "% sample!"

Then you could delete them like this:arcpy.MakeFeatureLayer(roadsFC, "delete_me", "OBJECTID in (" + str(randomSampleList)[1:-1] + ")")
arcpy.DeleteFeatures_Managment("delete_me")

or use an update cursor... same thing.

MatthiasBuehler1 · Answer

hey !

thanks a lot for that code, it works so far !

to understand what actually happens here is that all features are actually stored as they were in a geometrical grid and then you delete them based on that grid ?

is it also possible to just use a for loop and (possibly) delete each object based on a probability ? or are list based structures not possible ?

thx again so far !