A compact “if” statement using “or” operator

Question

Sim 2023-6-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1976674-a-compact-if-statement-using-or-operator

评论： Sim 2023-6-2

A more compact way to write the “if” statement using “or” operator, than this one?

if i == 1 || i == 2 || i == 7 || i == 8 || i == 10
    % ...
end

Something similar to this statement?

if i == [1 2 7 8 10]
    % ...
end

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Answer 1

Dyuman Joshi 2023-6-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1976674-a-compact-if-statement-using-or-operator#answer_1248279

编辑：Dyuman Joshi 2023-6-1

在 MATLAB Online 中打开

Yes there is - ismember

vec = [1 2 7 8 10];
i = 4;
%Checks if elements in i are present in vec or not
ismember(i,vec)
ans = logical
   0
if ismember(i,vec)
    disp('if')
else
    disp('else')
end
else

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James Tursa 2023-6-1

编辑：James Tursa 2023-6-1

在 MATLAB Online 中打开

You can also use this FEX submission anyEq by Jan for short circuiting mex approach:

https://www.mathworks.com/matlabcentral/fileexchange/26867-anyeq?s_tid=srchtitle

Which method is fastest is going to depend on the data. I am guessing that any( ) and ismember( ) may be short-circuiting and multi-threaded in the background, whereas anyEq( ) is only short-circuiting and not multi-threaded. For random data sets, maybe the middle element match is the best single point comparison. In any event, here are the results on my PC using a modified timetesting routine. You can draw your own conclusions.

>> timetesting(1e5)
First element test ...
    Time taken by any for n = 100000 elements is 4.524267e-05 secs
Time taken by ismember for n = 100000 elements is 4.477289e-05 secs
Time taken by anyEq for n = 100000 elements is 4.171053e-06 secs
Middle element test ...
    Time taken by any for n = 100000 elements is 3.773170e-05 secs
Time taken by ismember for n = 100000 elements is 3.633585e-05 secs
Time taken by anyEq for n = 100000 elements is 5.452644e-05 secs
Last element test ...
    Time taken by any for n = 100000 elements is 4.850370e-05 secs
Time taken by ismember for n = 100000 elements is 5.633299e-05 secs
Time taken by anyEq for n = 100000 elements is 1.259781e-04 secs
>> timetesting(1e6)
First element test ...
Time taken by any for n = 1000000 elements is 4.766502e-04 secs
Time taken by ismember for n = 1000000 elements is 8.393297e-04 secs
Time taken by anyEq for n = 1000000 elements is 4.046598e-06 secs
Middle element test ...
Time taken by any for n = 1000000 elements is 6.579002e-04 secs
Time taken by ismember for n = 1000000 elements is 4.371002e-04 secs
Time taken by anyEq for n = 1000000 elements is 5.775002e-04 secs
Last element test ...
Time taken by any for n = 1000000 elements is 1.343650e-03 secs
Time taken by ismember for n = 1000000 elements is 9.622297e-04 secs
Time taken by anyEq for n = 1000000 elements is 1.145030e-03 secs
>> timetesting(1e7)
First element test ...
    Time taken by any for n = 10000000 elements is 7.754430e-03 secs
Time taken by ismember for n = 10000000 elements is 7.475530e-03 secs
Time taken by anyEq for n = 10000000 elements is 4.097298e-06 secs
Middle element test ...
    Time taken by any for n = 10000000 elements is 8.172130e-03 secs
Time taken by ismember for n = 10000000 elements is 8.390230e-03 secs
Time taken by anyEq for n = 10000000 elements is 5.566130e-03 secs
Last element test ...
    Time taken by any for n = 10000000 elements is 1.057803e-02 secs
Time taken by ismember for n = 10000000 elements is 9.976730e-03 secs
Time taken by anyEq for n = 10000000 elements is 1.105403e-02 secs
>> timetesting(1e8)
First element test ...
Time taken by any for n = 100000000 elements is 7.226343e-02 secs
Time taken by ismember for n = 100000000 elements is 7.215803e-02 secs
Time taken by anyEq for n = 100000000 elements is 3.966129e-06 secs
Middle element test ...
Time taken by any for n = 100000000 elements is 8.314263e-02 secs
Time taken by ismember for n = 100000000 elements is 7.997993e-02 secs
Time taken by anyEq for n = 100000000 elements is 5.639903e-02 secs
Last element test ...
Time taken by any for n = 100000000 elements is 9.267643e-02 secs
Time taken by ismember for n = 100000000 elements is 9.262103e-02 secs
Time taken by anyEq for n = 100000000 elements is 1.115631e-01 secs

And the code:

function timetesting(n)
vec = rand(n,1);
%any
f1 = @(a,b) fun1(a,b);
%ismember
f2 = @(a,b) fun2(a,b);
%anyEq
f3 = @(a,b) fun3(a,b);
% First element test
disp('First element test ...')
y = vec(1);
F1 = @() f1(y, vec);
F2 = @() f2(y, vec);
F3 = @() f3(y, vec);
fprintf('Time taken by any for n = %d elements is %d secs\n', n, timeit(F1))
fprintf('Time taken by ismember for n = %d elements is %d secs\n', n, timeit(F2))
fprintf('Time taken by anyEq for n = %d elements is %d secs\n', n, timeit(F3))
% Middle element test
disp('Middle element test ...')
y = vec(round(n/2));
F1 = @() f1(y, vec);
F2 = @() f2(y, vec);
F3 = @() f3(y, vec);
fprintf('Time taken by any for n = %d elements is %d secs\n', n, timeit(F1))
fprintf('Time taken by ismember for n = %d elements is %d secs\n', n, timeit(F2))
fprintf('Time taken by anyEq for n = %d elements is %d secs\n', n, timeit(F3))
% First element test
disp('Last element test ...')
y = vec(end);
F1 = @() f1(y, vec);
F2 = @() f2(y, vec);
F3 = @() f3(y, vec);
fprintf('Time taken by any for n = %d elements is %d secs\n', n, timeit(F1))
fprintf('Time taken by ismember for n = %d elements is %d secs\n', n, timeit(F2))
fprintf('Time taken by anyEq for n = %d elements is %d secs\n', n, timeit(F3))
    function z1 = fun1(y,vec)
        z1=any(y==vec);
    end
    function z2 = fun2(y,vec)
        z2=ismember(y,vec);
    end
    function z3 = fun3(y,vec)
        z3=anyEq(y,vec);
    end
end

Dyuman Joshi 2023-6-1

编辑：Dyuman Joshi 2023-6-1

在 MATLAB Online 中打开

It is interesting to note that anyEq() is the fastest for first element and the slowest for the last element, and there timings of any() and ismember() are similar.

Edit - In the Overview section of the FileEx submission, Jan mentions - "Best case (first element matches): 99.99% faster for 1e6 elements (Matlab 2011b/64, MSVC 2008)"

%From the above tests done by James Tursa
n_any = 4.766502e-04;
n_is = 8.393297e-04;
n_eq = 4.046598e-06;
1-n_eq/n_any
ans = 0.9915
1-n_eq/n_is
ans = 0.9952