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What methods are available in ArcGIS 10.2 to randomly subset a selection of points. For example, in the attached screenshot I am interested in keeping 20% of the selected points and deleting the rest.

enter image description here

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Well I don't think there is a default method for selecting random points from layer. Did you try with python script? Or add-in? –  Marcin D Nov 21 '13 at 20:08

4 Answers 4

You could try Hawth's Tools: http://www.spatialecology.com/htools/rndsel.php

Note that the existing selection is not honored so you would have to make a feature layer from the existing selection first.

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Unfortunately, that version isn't compatible with ArcGIS 9.3 and above. Now it's called Geospatial Modelling Environment: spatialecology.com/gme –  kenbuja Nov 21 '13 at 21:33
    
Good point, here is the equivalent command in GME: spatialecology.com/gme/rsample.htm –  blah238 Nov 21 '13 at 21:43

There is also an earlier Select features at random script from Stephen Lead available for ArcGIS Desktop. Although written, I think, for ArcGIS 9.x, and last modified in 2008, I used it in about 2010 at 10.0, and it still worked well.

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Generally, I also recommend using the spatial ecology tools as discussed by blah238.

However, another method you could try would be to add an attribute called Random to store a random number: enter image description here

Then, using the field calculator on that attribute, with the Python Parser, use the following codeblock:

import random
def rand():
  return random.random()

See image below:

This will create random values between 0 and 1. Then, if you want to select 20% of the features, you could select features where the Random value is less than 0.2. Of course, this will work better with many features. I created a feature class with only 7 features as a test and there were no values less than 0.2. However, it looks like you have plenty of features, so that shouldn't matter.

enter image description here

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this method will return on average 20% of the features, which in some cases would be preferred. But if you want 20% every time, you can do as suggested, then sort the features by the random value and select the first 20%. –  Llaves Nov 22 '13 at 4:04

Here's another random selection add-in for ArcGIS 10, the Sampling Design Tool. It will let you select 20% of the features in your dataset. However, this doesn't use a selected set to make a random selection, similar to the restrictions of the Hawth's Tools mentioned by blah238.

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