How to find out if a logical array is all zeros?

I have a logical array that is 100x1 logical. sometimes it contains a mix of numbers and sometimes it contains all 0s.

How would i go about making an if statement that checks to see if all 100x1 is 0s and if all 0s = do something

I thought i was correct in using any command but im not sure that works correctly for me..

Thanks!

[Walter Roberson]

rise() is an undefined function.

Answer 1

[John D'Errico]

any does work, with a slight tweak. But you could also use all, or sum, or nnz, or even find. There are certainly many ways.

if ~any(X)
   ...
end

if all(~X)
   ...
end

if sum(x) == 0
   ...
end

if numel(find(x)) == 0
   ...
end

if nnz(x) == 0
   ...
end

Any of those tools would suffice.

[Stephen23]

In general the most efficient approach is likely to be ~any(X):

X = false(1,1e7);
X([1e3,end]) = true;

timeit(@()~any(X))

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 1.8459e-07

timeit(@()all(~X))

ans = 0.0010

timeit(@()sum(X)==0)

ans = 0.0011

timeit(@()numel(find(X))==0)

ans = 0.0089

timeit(@()nnz(X)==0)

ans = 6.8383e-04

[James Tursa]

Note that any( ) is possibly written to short-circuit in the background, as these timings suggest:

x = false(1,100000000);
y = x;
x(end) = true; % last element is true
y(1) = true; % first element is true
timeit(@()~any(x)) % has to examine all of the elements to find the true one?

ans = 0.0230

timeit(@()~any(y)) % once first element is examined the answer is known

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

[Walter Roberson]

@James Tursa

No, it is just very fast at checking from the beginning of the array.

Some of my tests on y show times on the order of 1e-9 instead of 0, by the way.

x = false(1,100000000);
y = x;
x(end) = true; % last element is true
y(1) = true; % first element is true
timeit(@()~any(x)) % has to examine all of the elements to find the true one?

ans = 0.0234

timeit(@()~any(y)) % once first element is examined the answer is known

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

timeit(@()~any(y)) % once first element is examined the answer is known

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

y(5000) = true;
timeit(@()~any(y)) % has to examine all of the elements to find the true one?

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

timeit(@()~any(y)) % once first element is examined the answer is known

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

timeit(@()~any(y)) % once first element is examined the answer is known

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

y(1) = true;
timeit(@()~any(y))

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

timeit(@()~any(y))

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

timeit(@()~any(y))

Warning: The measured time for F may be inaccurate because it is running too fast. Try measuring something that takes longer.

ans = 0

y(1) = false;
timeit(@()~any(y)) % once first element is examined the answer is known

ans = 1.0476e-06

timeit(@()~any(y)) % once first element is examined the answer is known

ans = 1.0646e-06

timeit(@()~any(y)) % once first element is examined the answer is known

ans = 1.0516e-06

Answer 2

[Turlough Hughes]

One way:

~any(x)

Answer 3

[William Rose]

@MKM,

If A is a vector,

sum(abs(A))

will be zero, or not, of all the elements are zero, or not.

If A is a 2D array, do

sum(sum(abs(A)))

Answer 4

[David Hill]

if all(~yourArray)

Answer 5

[Steven Lord]

For a vector, all with one input will work.

x = ones(10, 1);
all(x > 0) % true

ans = logical
   1

For a non-vector array you probably want to specify a dimension. In recent releases, you can specify a vector of dimensions on which to operate or you can specify 'all' as the dimension to operate on all the dimensions no matter how many there are.

x = ones(10, 10);
all(x > 0) % Only operate on dimension 1

ans = 1×10 logical array
   1   1   1   1   1   1   1   1   1   1

all(x > 0, 'all') % Operate on dimensions 1 and 2

ans = logical
   1

x = ones(10, 10, 10);
all(x > 0, [1 3]) % Operate on dimensions 1 and 3

ans = 1×10 logical array
   1   1   1   1   1   1   1   1   1   1

all(x > 0, 'all') % Operate on dimensions 1, 2, and 3

ans = logical
   1

[MKM]

This is great! Thanks for taking the time to help me with this.