Re: boolean indexing for subset reassignment
- To: mathgroup at smc.vnet.net
- Subject: [mg132616] Re: boolean indexing for subset reassignment
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Mon, 21 Apr 2014 05:12:04 -0400 (EDT)
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- Delivered-to: l-mathgroup@wolfram.com
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On 4/20/14 at 4:47 AM, alan.isaac at gmail.com (Alan) wrote: >Two years ago this answer was given: >http://mathematica.stackexchange.com/questions/2821/does-mathematica >-have-advanced-indexing >Essentially, the answer was that Mathematica did not provide direct >support for this feature (unlike say NumPy, R, etc.). Work arounds >were suggested. >Has the situation changed? No, there is no built-in function that does just what was described. But this is a very simple thing to do in Mathematica. generate an array with some values greater than 15: In[3]:= a = RandomInteger[{1, 20}, {4, 3}] Out[3]= {{12, 6, 17}, {4, 17, 19}, {14, 10, 7}, {8, 2, 15}} generate the array to change: In[4]:= b = RandomReal[1, {4, 3}] Out[4]= {{0.6304544421081466, 0.10672523812862322, 0.4822372961689563}, {0.06301096415944252, 0.975158725702236, 0.052202491707093346}, {0.06883790695346681, 0.7890506831190796, 0.8367965617051536}, {0.8641752609839166, 0.6371442124093818, 0.9217402690944818}} then In[5]:= m = b Unitize@Clip[a, {1, 15}, {0, 0}] Out[5]= {{0.6304544421081466, 0.10672523812862322, 0.}, {0.06301096415944252, 0., 0.}, {0.06883790695346681, 0.7890506831190796, 0.8367965617051536}, {0.8641752609839166, 0.6371442124093818, 0.9217402690944818}} is array b changed to have a 0 wherever the corresponding element of a is greater than 15