Random selection of XY% of points within fishnet cells in ArcGIS Pro

Question

I am using ArcGIS Pro and have a feature class of approx. 30.000 points and a polygon grid. Within each grid cell I want to select XY% (50, 70 or any other percentage) of the points (see picture).

I am referring to this - what would I change in the code to select a dynamic number of points within the grid cell?

Answer 1

Based on the link you provided, you'd want to define a sample_percent instead of a sample_size. Then, when iterating over groups.items(), you'd define sample_size by rounding up the number of points times your percent. Something like this:

import arcpy, random
from collections import defaultdict
from math import ceil

points = 'points' #Layer name
groupfield = 'fishnet_id' #Some id identifying each fishnet cell
sample_percent = 0.5  #Percent (0-1) of points in each cell to select

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.items():
    sample_size = ceil(len(value)*sample_percent)
    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)