Code not working when putting in 1:length(X), but code is working when putting the value of length(X)

Hi,

I've situation, and I really don't what the reason for this error is. I want to define a cells in a cell. Herefore a made a for-loop in a for-loop So I have the following code:

processed_segment = cell(3,1);
processed_stage   = cell(1,6);
for stage = 1:6
    stage_patient = patientsignal{1,stage};
    length_stage = length(stage_patient);
    numberOfSegment = int16(length_stage/Nsegment);
    processed_signal = cell(1, numberOfSegment-1);
    for z = 1:73
        [iECG,fECG,SQI, segmentpatient] = FINALECG_Stage(patientdata, patientnumber, stage ,Nsegment,Fs,Measurement, z);
        processed_segment{1,1} = iECG;
        processed_segment{2,1} = fECG;
        processed_segment{3,1} = SQI;
        processed_signal{1,z} = processed_segment;
        segmentpatient = segmentpatient;
    end
processed_stage{1, stage} = processed_signal;
end

In the second for-loop you see z variable.

When I use " z = 1 : 73 ", the code is working fine and its executes the loop as wished.

But when I use " z = 1 : numberOfSegment ", and in this case the value of numberOfSegment is 73, I get the following error:

Error using welchparse>segment_info (line 258)

The length of the segments cannot be greater than the length of the input signal.

..... just why tho? What is the reason?

[Ameer Hamza]

What are the dimensions of stage_patient?

[Enes Kinaci]

Each stage contains an array of " X (samples) row by 1 column". But the X samples differs per stage. That is why I calculate the length of the array for each stage. With:

    stage_patient = patientsignal{1,stage};
    length_stage = length(stage_patient);

Each stage is between 100.000 and 700.000 samples. Depending on the number of samples, the array is being segmented in arrays of 10.000 samples (Nsegment = 10.000).

With the following code, I calculate the number of segments that occurs based on the X samples.

    numberOfSegment = int16(length_stage/Nsegment);

Suppose I have a stage which contains an array of (730.000 x 1). Then, the number of segments that I get is 73. I want to process and analyze each of this segment seperately. The second for-loop is used for selecting each segment seperately.

My problem is: If I write " for z = 1 : numberOfSegments ", the code is not working after 4 iterations. But when I put " z = 1 : 73 " the whole loop is being executed (73 iterations), and goes to the next stage (executing the first for-loop).

[Ameer Hamza]

Such problems can easily be solved using breakpoints: https://www.mathworks.com/help/matlab/matlab_prog/set-breakpoints.html. Add a breakpoint at the line

for z = 1:numberOfSegment

from that point, run the code line by line. You will see which line causes an unexpected behavior causing the loop to terminate.

Answer 1

[Ameer Hamza]

length() function call can be ambiguous and create the potential of such errors when used carelessly. Instead, use size(): https://www.mathworks.com/help/releases/R2020a/matlab/ref/size.html and explicitly specify the dimension.

[Stephen23]

+1 length should be obsoleted.

Answer 2

[Image Analyst]

It's probably because the patientsignal cell array does not have 73 cells in it. I've tried to put in some checks and make the code more robust below, but of course I can't test it because you didn't include data or the top part of your program.

processed_segment = cell(3,1); % 1-D column vector of cells.
processed_stage   = cell(1,6); % 1-D row vector of cells.
for stage = 1 : 6
    % Get the contents of the "stage" column of row 1 of patientsignal.
    stage_patient = patientsignal{1,stage}; 
    length_stage = length(stage_patient);
    % Above line of code assumes stage_patient is a 1-D vector.  Let's check to make sure.
    [rows, columns] = size(stage_patient);
    fprintf('stage_patient has %d rows and %d columns.\n', rows, columns);
    if ~(rows == 1 || column == 1)
        warningMessage = sprintf('Hey!\nstage_patient is not a vector -- it is a matrix.\nstage_patient has %d rows and %d columns.\n', rows, columns);
        uiwait(warndlg(warningMessage));
    end
    numberOfSegments = int16(length_stage/Nsegment);
    fprintf('    Stage %d has %d segments.\n', numberOfSegments);
    processed_signal = cell(numberOfSegments); % 1-D vector of cells.
    for z = 1 : numberOfSegments
        [iECG, fECG, SQI, segmentpatient] = FINALECG_Stage(patientdata, patientnumber, stage ,Nsegment,Fs,Measurement, z);
        processed_segment{1,1} = iECG;
        processed_segment{2,1} = fECG;
        processed_segment{3,1} = SQI;
        processed_signal{1,z} = processed_segment;
    end
    processed_stage{1, stage} = processed_signal;
end

[Enes Kinaci]

Each stage contains an array of " X (samples) row by 1 column". But the X samples differs per stage. That is why I calculate the length of the array for each stage. With:

    stage_patient = patientsignal{1,stage};
    length_stage = length(stage_patient);

Each stage is between 100.000 and 700.000 samples. Depending on the number of samples, the array is being segmented in arrays of 10.000 samples (Nsegment = 10.000).

With the following code, I calculate the number of segments that occurs based on the X samples.

    numberOfSegment = int16(length_stage/Nsegment);

Suppose I have a stage which contains an array of (730.000 x 1). Then, the number of segments that I get is 73. I want to process and analyze each of this segment seperately. The second for-loop is used for selecting each segment seperately.

My problem is: If I write " for z = 1 : numberOfSegments ", the code is not working after 4 iterations. But when I put " z = 1 : 73 " the whole loop is being executed (73 iterations), and goes to the next stage (executing the first for-loop).

[Image Analyst]

Did you see where I said "of course I can't test it because you didn't include data or the top part of your program."?