Comments on: ismembc – undocumented helper function http://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/ Charting Matlab's unsupported hidden underbelly Thu, 09 Feb 2012 09:23:08 +0000 hourly 1 http://wordpress.org/?v=3.1.1 By: Yair Altmanhttp://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/#comment-58796 Yair Altman Thu, 06 Oct 2011 20:14:42 +0000 http://undocumentedmatlab.com/?p=164#comment-58796 @Vivien - the preconditions required by <b><i>ismembc</i></b> were indeed mentioned in the article:<b><i>ismembc</i></b> should not be used carelessly: as noted, its inputs must be sorted non-sparse non-NaN values. In the general case we should either ensure this programmatically (as done in <b><i>setxor</i></b>) or use <b><i>ismember</i></b>, which handles this for us. @Vivien – the preconditions required by ismembc were indeed mentioned in the article:

ismembc should not be used carelessly: as noted, its inputs must be sorted non-sparse non-NaN values. In the general case we should either ensure this programmatically (as done in setxor) or use ismember, which handles this for us.

]]> By: Vivienhttp://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/#comment-58773 Vivien Thu, 06 Oct 2011 08:04:58 +0000 http://undocumentedmatlab.com/?p=164#comment-58773 It doesn't work if it's not sorted. The function stops as soon as it meets a higher value. The given example is bad because the function stops most of the time too early (but ismembc is indeed faster). <pre lang='matlab'> >> a = [3,5]; b = [1,2,3,4,9,5]; >> ismembc(a,b) ans = 1 0 </pre> It doesn’t work if it’s not sorted. The function stops as soon as it meets a higher value. The given example is bad because the function stops most of the time too early (but ismembc is indeed faster).

>> a = [3,5]; b = [1,2,3,4,9,5];
>> ismembc(a,b)
ans =
     1     0
]]> By: Undocumented Matlab at Nordt Bloghttp://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/#comment-54334 Undocumented Matlab at Nordt Blog Thu, 18 Aug 2011 09:35:08 +0000 http://undocumentedmatlab.com/?p=164#comment-54334 [...] and infos. (Click here) Especially the performance // hidden functions are to be looked at. The ismembc2 tipp, hell yeah « One [...] [...] and infos. (Click here) Especially the performance // hidden functions are to be looked at. The ismembc2 tipp, hell yeah « One [...]

]]> By: Robhttp://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/#comment-45884 Rob Thu, 02 Jun 2011 00:17:48 +0000 http://undocumentedmatlab.com/?p=164#comment-45884 interestingly, it appears that the variable "a" does not have to be sorted for using ismembc(), but the algorithm runs much more quickly if it is. interestingly, it appears that the variable “a” does not have to be sorted for using ismembc(), but the algorithm runs much more quickly if it is.

]]> By: Datenum performance | Undocumented Matlabhttp://undocumentedmatlab.com/blog/ismembc-undocumented-helper-function/#comment-42711 Datenum performance | Undocumented Matlab Thu, 05 May 2011 18:37:37 +0000 http://undocumentedmatlab.com/?p=164#comment-42711 [...] This question reminded me of a similar case that I answered exactly two years ago, of improving the performance of the built-in <i><b>ismember</b></i> function. In both cases, the solution to the performance question can be found by simply using Matlab's built-in profiler in order to extract just the core processing functionality. [...] [...] This question reminded me of a similar case that I answered exactly two years ago, of improving the performance of the built-in ismember function. In both cases, the solution to the performance question can be found by simply using Matlab’s built-in profiler in order to extract just the core processing functionality. [...]

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