select random points

01-30-2014 07:19 PM
New Contributor
Hey all!

I have sounding data with tens of thousands of points per feature. I need to reduce the points significantly in density, and was hoping there was a way to randomly select points through an arcmap tool. While the create random points tool does what I need, it does not seem to maintain the attribute data (eg. depth) that I need with each point. Any suggestions?
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7 Replies
Occasional Contributor II
I think the Create Random Points tool does just that: creates new points randomly, rather than selecting existing points randomly.

You could try adding a new field to your existing points, then calculating a random 1 or 0 for each point, then just select out the 1s. I think it could still be a bit random how many 1s you get though, it might not reduce the points by much.

If there was a certain factor you wanted to reduce the data by, and as long as the OBJECT_IDs aren't sorted in any way, you could calculate a modulo in your field, e.g. to just pick out every 10th point, you'd calculate OBJECT_ID % 10 (which would give you the remainder left if you divided the OBJECT_ID by 10) and select all the 0s in that field.

Hope that makes sense, if not let me know and I will try to explain better!

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Esri Regular Contributor
Subset Features is designed to do that.
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Occasional Contributor III
Subset Features is designed to do that.

*** Requires Geostatistical Analyst ***
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Occasional Contributor III
This code will populate an existing attribute with a random number.  Run the script.  Then, for example, select values less than 0.2 to select about 20% of your points.

#Populates an existing attribute with a randomly generated value 

    import operator, os, random, traceback, sys, arcpy
    arcpy.AddMessage("Adding random numbers to an existing attribute.")
    arcpy.AddMessage("Copyright 2011, Gerry Gabrisch,")

    #Path to the feature class.
    fc = arcpy.GetParameterAsText(0)
    #The Attribute to populate...
    attribute = arcpy.GetParameterAsText(1)
    uc = arcpy.UpdateCursor(fc)
    for row in uc:
        x = random.random()
        row.setValue(attribute, x)
except arcpy.ExecuteError: 
    msgs = arcpy.GetMessages(2)
    tb = sys.exc_info()[2]
    tbinfo = traceback.format_tb(tb)[0]
    pymsg = "PYTHON ERRORS:\nTraceback info:\n" + tbinfo + "\nError Info:\n" + str(sys.exc_info()[1])
    msgs = "ArcPy ERRORS:\n" + arcpy.GetMessages(2) + "\n"
    arcpy.AddMessage(pymsg + "\n")
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New Contributor III

I'm guessing you're eight years beyond needing an answer to this question. But here is some more info: In ArcGIS Pro 2.8, you can use the Create Random Points tool to select a subset, using your original point feature class as the "Constraining Feature Class". The attributes are not preserved in the output as you note; however, you can join via the CID field, matching to the OID in the original data source.

by Anonymous User
Not applicable

Or select by location using the new feature as the intersecting feature!

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