Randomly selecting single point from within multiple fishnet grid-squares?

Question

Using ArcGIS, I have a large data set of occurrence data many of which are in similar places. I have created a fishnet around the total area and want to select a single random point from within each grid-square of the fishnet.

How do I go about this?

I want to run this multiple times so that I can then bootstrap it. I know I could subset each individual grid-square but there are approximately 100 of them so this would take a very long time.

Answer 1

You can use arcpy to randomly select points by some group attribute. In your case fishnet id.

First Intersect Points with fishnet to get a fishnet id attribute on all Points.

Then modify the commented lines and execute this in the Python window with the point layer added to the map:

import arcpy, random
from collections import defaultdict

points = 'points' #Layer name
groupfield = 'fishnet_id' #Some id identifying each fishnet cell
sample_size = 1 #Points to select per group

oidfield = arcpy.Describe(points).OIDFieldName

groups = defaultdict(list)

with arcpy.da.SearchCursor(points, [groupfield, oidfield]) as cursor:
    for key,value in cursor:
        groups[key].append(value)

oidlist = []
for key,value in groups.iteritems(): # use groups.items() for ArcGIS Pro/py3
    oidlist.extend(random.sample(value,sample_size))

sql = """{0} IN({1})""".format(arcpy.AddFieldDelimiters(points,oidfield), ','.join([str(i) for i in oidlist]))
arcpy.SelectLayerByAttribute_management(points, where_clause=sql)