A compact “if” statement using “or” operator

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

Answer 1

[Dyuman Joshi]

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

[Sim]

thanks a lot @Dyuman Joshi!

[Stephen23]

An efficient approach with ANY():

if any(i==[1,2,7,8,10])

[Dyuman Joshi]

@Stephen23, testing the time taken by both approachs wields similar results, with ismember() having slightly better run time

timetesting(1e5)

Time taken by any for n = 100000 elements is 7.782450e-05 secs
Time taken by ismember for n = 100000 elements is 6.332450e-05 secs

ans = logical
   1

timetesting(1e7)

Time taken by any for n = 10000000 elements is 7.391765e-03 secs
Time taken by ismember for n = 10000000 elements is 7.042764e-03 secs

ans = logical
   1

function timetesting(n)
vec = rand(n,1);
y = vec(randi(n));

%any
f1 = @(a,b) fun1(a,b);
%ismember
f2 = @(a,b) fun2(a,b);

F1 = @() f1(y, vec);
F2 = @() f2(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))

isequal(F1(),F2())

function z1 = fun1(y,vec)
z1=any(y==vec);
end

function z2 = fun2(y,vec)
z2=ismember(y,vec);
end
end

[James Tursa]

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

[DGM]

Since we're comparing floats, a similar comparison can be made between ismembertol() and

z = any(abs(y-vec) <= tol)

In this case (at least with my testing), the advantage of the rudimentary comparison is much more significant (a couple orders of magnitude).

[Dyuman Joshi]

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

And it still holds.

[Sim]

thanks to everyone, @Dyuman Joshi @Stephen23 @James Tursa @DGM, for your comments!