Need to get dimensions to match and to return a 0 x 0 matrix for empty row.

This code give me a 1 x 0 array for any row that is empty. I need it to return a 0 x 0 empty matrix for any row that is empty. It is presently giving me an error and proclaiming that the dimensions of the object in the "if" statement don't match.

function S = logipack( V)
m = size(V, 1);
S = cell(m, 1);
for r = 1:m
   S{r} = find(V(r, :));
   if find(V(r,:))==[]
       S{r}= [];
   end
end
end

[the cyclist]

What data type is V?

[Geoff Hayes]

DJ - this is the third time that you have posted a question that deals with the same problem of writing the logipack function. Why not continue at https://www.mathworks.com/matlabcentral/answers/317178-what-is-wrong-with-this or https://www.mathworks.com/matlabcentral/answers/317062-told-to-ask-a-new-question-why-won-t-this-work?

Also, consider using the MATLAB debugger to step through the code to understand what is happening. See https://www.mathworks.com/help/matlab/debugging-code.html for details.

[DJ V]

Because each question represents some advancement, as I was advised earlier by another poster. I am therefore posting each stage of advancement, in the hope of attracting helpful attention. It is a matter of coming to understand how to do specific things, such as saving an empty matrix with dimensions 0 x 0 and not violating how Matlab represents this in terms of syntax.

[DJ V]

V is a matrix of 1's and 0's. IF there is a 1 in a row the logipack software is supposed to identify the column numbers where it occurs. If there are no 1's, the software is supposed to return an empty vector of size 0 x 0.

[Jan]

@DJ V: You discus the problem "find(V(r,:))==[]" here, although the answer I've given at https://www.mathworks.com/matlabcentral/answers/317178-what-is-wrong-with-this#answer_247497 contains the correct isempty() already. By this way, you do not catch attraction, but discourage readers to care about your questions.

Answer 1

[John BG]

DJ

MATLAB moans, not because of if condition mismatch, but because the operator '==' doesn't work for cells, try this:

cell1 = 
    'a'    [1]    '9'    [2x2 double]
>> cell2={'b' 2}
cell2 = 
    'b'    [2]
>> cell1==cell2
Undefined operator '==' for input arguments of type 'cell'.

So,

1.- your 1st line in the for loop doesn't make much sense,

S{r} = find(V(r, :))

so I changed it to

   S{r} = V(r, :)

may be it's not what you want but at least now S is not empty.

2.- instead of

   if find(V(r,:))=={}

try

if isempty(V(r,:))

or better

if isempty(V(r))

So the following, although not sure whether of much use, at least it doesn't crash

V=randi([-10 10],1,10)

m = size(V, 2);
S = cell(m, 1);
for r = 1:m
   S{r} = V(r);
   if isempty(V(r))
       S{r}= [];
   end
end

if you find this answer useful would you please be so kind to mark my answer as Accepted Answer?

To any other reader, please if you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

[DJ V]

Not correct, in fact, your code undoes what I'm trying to do.

S{r} = find(V(r, :))

is central to the solution.

Isempty does work, but it again assigns a 1 x 0 empty vector and not a 0 x 0 empty vector. That is the problem to which I need to find a solution. Nothing else. I'll post the code again as it now stand, with the 1 x 0 empty vector being inserted for appropriate lines:

function out = logipack(V)
m = size(V, 1);
S = cell(m, 1);
for r = 1:m
   S{r} = find(V(r, :));
   m = size(V, 1);
    if isempty(V(r))
       S{r}= [];
    end
end
out = S;
end

[DJ V]

Just in case anyone is curious, this code works and passes the grader:

function out = logipack(V)
m = size(V, 1);
S = cell(m, 1);
for r = 1:m
   S{r} = find(V(r, :));      
end
for r = 1:m
    for q = 1:m
    if q==1
        count=0;
    end
    if V(r,q)==0
      count= count+1;
    end
    if count==m 
        S{r,1}=[];
    end 
    end
end
out = S;
end

[John BG]

happy to see you have managed to answer your own question, crack on

Answer 2

[the cyclist]

You can probably take advantage of the isempty command here.