Selecting points using random field values in ArcGIS Desktop?

Question

I have point layer, counties border area layer and I want to pick different number of points within different areas (counties) but from existing point layer - e.g. county A -> 10, county B -> 6, etc.

I'm wondering if code delivered by @Emil Brundage in Randomly subsetting X% of selected points using ArcPy? could be changed to use field values and area borders (like in Create Random Points tool) instead of one indicated count value to select random points from whole point layer. Because this code does only this.

Did I describe it clearly now?

def SelectRandomByCount (layer, count):
import random
layerCount = int (arcpy.GetCount_management (layer).getOutput (0))
if layerCount < count:
    print "input count is greater than layer count"
    return
oids = [oid for oid, in arcpy.da.SearchCursor (layer, "OID@")]
oidFldName = arcpy.Describe (layer).OIDFieldName
path = arcpy.Describe (layer).path
delimOidFld = arcpy.AddFieldDelimiters (path, oidFldName)
randOids = random.sample (oids, count)
oidsStr = ", ".join (map (str, randOids))
sql = "{0} IN ({1})".format (delimOidFld, oidsStr)
arcpy.SelectLayerByAttribute_management (layer, "", sql)

I've edited a little my question, maybe this time it would be easier to understand me :) — KaBi, Dec 05 '17 at 10:01
The desired number of selected Points are in a column in the county polygons? — BERA, Dec 05 '17 at 10:36
@BERA - yes, in that layer I have county name and number of points that are suppose to be picked. — KaBi, Dec 05 '17 at 11:19

score 1 · Answer 1 · answered Dec 05 '17 at 11:39

With a few modifications, it can be done. Eventually you need to specify the number of random point by the attribute (i.e. selection_dict below). Here is an example:

import arcpy

def SelectRandomByCount (layer, count):
    import random
    layerCount = int (arcpy.GetCount_management (layer).getOutput (0))
    count=layerCount if layerCount < count else count
    oids = [oid for oid, in arcpy.da.SearchCursor (layer, "OID@")]
    return random.sample (oids, count)

selection_dict={"County A":10,"County B":6}
aggregate_random_oids=[]

for k,v in selection_dict.items():
    arcpy.SelectLayerByAttribute_management(my_layer,"NEW_SELECTION","%s = '%s'" %(arcpy.AddFieldDelimiters(my_layer.dataSource,"County_Name"),k))
    aggregate_random_oids+=SelectRandomByCount (my_layer, v)

oidFldName = arcpy.Describe (my_layer).OIDFieldName
path = arcpy.Describe (my_layer).path
delimOidFld = arcpy.AddFieldDelimiters (path, oidFldName)
oidsStr = ", ".join (map (str, aggregate_random_oids))
sql = "{0} IN ({1})".format (delimOidFld, oidsStr)
arcpy.SelectLayerByAttribute_management (my_layer, "", sql)

Selecting points using random field values in ArcGIS Desktop?

1 Answers1