Are enum-comparisons slow in MATLAB?

Question

Joakim Näsström 2019-11-11

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编辑： Joakim Näsström 2020-6-24

采纳的回答： per isakson

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Hi,

For everyone to know which MATLAB verison I am running , this is it: MATLAB Version: 9.5.0.944444 (R2018b).

My question is simple, Should i or should i not use enumerations in MATLAB if performance is important?

Im my code, i have the following object and enumeration defined

classdef Object < handel
    properties
        Dependency (1,1) DependencyType
    end
end
classdef DependencyType < uint8
    enumeration
        NONE  (0)
        LOWER (1)
        UPPER (2)
    end
end

The class have a property called Dependency whouch should be of type DependencyType and DependencyType is an enumeration and a subclass of uint8.

In another function, not a member of the class, i have an if-statement that looks like follows

if obj.Dependency == DependencyType.NONE
    ...
end

When I am running the profiler, the if-statement line takes up 35% of the execution time of the function, the function is called 100000 ish times. I wonder if using enumerations in MATLAB is slow or if this is just an overhead of the profiler? I have not found any information regarding this while looking on the internet! I cant understand why it would be slow since there should not be any type conversions. So it must be due to profiling being turned on, but I cant be sure!

If this is not just some overhead from the profiler, then whats wrong. Is it constantly createing new DependencyType objects in the if-statement? Am I doing the comparison wrongly? Why does the comparison take so long time compared to the rest of the code that is way more computationaly demanding in the function.

Best regards

Joakim

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Jan Siegmund 2020-3-22

Same here. The profiler shows massive time consumption in converting the enums to a number to finally compare it. I'll go back to regular integer comparison.

Jan Siegmund 2020-3-22

Code with 30mio calls to such a comparison: 30min with bare numbers, 2:15h with enum comparison. Thats a dealbreaker.

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Answer 1

per isakson 2020-5-27

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https://ww2.mathworks.cn/matlabcentral/answers/490429-are-enum-comparisons-slow-in-matlab#answer_439808

编辑：per isakson 2020-5-27

在 MATLAB Online 中打开

Indeed, enumerations make slow code.

This is an anecdote about a code based on enumeration that proved useless because of poor performance and a happy end.

I created a class to classify characters of m-code. I made it an excerise in Finite State Machine. I used one enumeration class for State and another for Input. It was a joy to work with enumeration and the resulting code is very readable. Then came the shock, the execution time was just unacceptable. Profiling didn't really help much.

Happy End

With a minor effort I improved the speed of the code by more than two orders of magnitude. First I replaced the enumeration classes by value classes with constant properties. Second I had to do a few minor changes in the main class. Third, since the profiler now produced better information, I modified two red lines.

Thus, I replaced

classdef 	InputTypes < uint8
    enumeration                         
        null_input          (  0 )
        single_quote        (  1 )
        double_quote        (  2 )
        opening_bracket     (  3 )
        closing_bracket     (  4 )
        delimiter           (  5 )
        ...
    end
end

by

classdef 	InputTypes  
    properties ( Constant = true )
        null_input      =  0;
        single_quote    =  1;
        double_quote    =  2;
        opening_bracket =  3;
        closing_bracket =  4;
        delimiter       =  5;
        ...
    end
end

and

classdef 	CharacterTypes < uint8
    enumeration
        null_statement              ( 0 )
        end_of_statement            ( 1 )
        code_outside_brackets       ( 2 )
        code_in_brackets            ( 3 )
        in_character_constant       ( 4 )
        in_string_constant          ( 5 )
        in_single_line_comment      ( 6 )
    end
end

by

classdef 	CharacterTypes 
    properties ( Constant = true )
        null_statement         = 0;
        end_of_statement       = 1;
        code_outside_brackets  = 2;
        code_in_brackets       = 3;
        in_character_constant  = 4;
        in_string_constant     = 5;
        in_single_line_comment = 6;
    end
end

I use R2018b. Accourding to what I read in the release notes the performance of enumeration has not been improved.

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Joakim Näsström 2020-6-24

编辑：Joakim Näsström 2020-6-24

Hi, since the answer came in late I had to do something bofore that. I ended up removing all enumerations and switched to use hardcoded integers instead. Using classes as you did with constant fields might have been a better solution but maybe for next code refactoring :)

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Answer 2

Anurag Pratap Singh 2020-6-23

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Hiii Joakim

I understand that you are trying to use enum in your code and are doubtful if that is slow

The underlying type of an enumeration is an integral type and the compiler converts the enum to an int type.So type conversions may take some time But that is neglibile or unnoticeabe

Please refer to https://www.mathworks.com/help/matlab/matlab_oop/enumerations.html enums documentation for more info on the enum classl

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per isakson 2020-6-23

"So type conversions may take some time But that is neglibile or unnoticeabe." implies that I made a gross mistake in the use of enumerations, which is the background to my answer.

Joakim Näsström 2020-6-24