Calculate Field Python examples—ArcGIS Pro | Documentation
Do a field calculation, setting your distribution to Uniform
Emulate the syntax from the help topic, but replace random.random with random.uniform.
import numpy as np
def getRandomValue():
return np.random.uniform()
Each value (defaults to between 0 and 1) has an equal chance of being drawn.
When you have calculated the whole field, simply do a query on that field querying for values < 0.2
That will pull 20% of the samples.
Alternately you can mess with > 0.8 or any other 20% range you like
... sort of retired...