Help with syntax for a self-made function

Question

Teshan Rezel 2021-8-12

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https://ww2.mathworks.cn/matlabcentral/answers/897092-help-with-syntax-for-a-self-made-function

评论： Teshan Rezel 2021-8-16

Hi folks,

I have the following function defined in Matlab but am getting an error when running. The error and the code are below. May I please ask for help with debugging this?

Thanks in advance

function fields = populateFields(index, structure)     
    Area(index) = getfield(structure, 'Area');
    MajorAxisLength(index) = getfield(structure, 'MajorAxisLength');
    MinoeAxisLength(index) = getfield(structure, 'MinorAxisLength');
    Eccentricity(index) = getfield(structure, 'Eccentricity');
    Orientation(index) = getfield(structure, 'Orientation');
    ConvexArea(index) = getfield(structure, 'ConvexArea');
    Circularity(index) = getfield(structure, 'Circularity');
    EquivDiameter(index) = getfield(structure, 'EquivDiameter');
    Solidity(index) = getfield(structure, 'Solidity');
    Extent(index) = getfield(structure, 'Extent');
    Perimeter(index) = getfield(structure, 'Perimeter');
    MaxFeretDiameter(index) = getfield(structure, 'MaxFeretDiameter');
    MaxFeretAngle(index) = getfield(structure, 'MaxFeretAngle');
    MinFeretDiameter(index) = getfield(structure, 'MinFeretDiameter');
    MinFeretAngle(index) = getfield(structure, 'MinFeretAngle'); 
end

function call:

[matrix, numObjects] = bwlabel(mask1);
rg = regionprops(matrix, 'all');
fields = populateFields(1, rg);

The error:

Output argument "fields" (and maybe others) not assigned during call to "Threshold>populateFields".

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Answer 1

Simon Chan 2021-8-12

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https://ww2.mathworks.cn/matlabcentral/answers/897092-help-with-syntax-for-a-self-made-function#answer_765737

编辑：Simon Chan 2021-8-12

You have not define your output variable 'fields' in your function, so nothing returns from the function

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Simon Chan 2021-8-12

在 MATLAB Online 中打开

It depends on how you would like to be the format and type of the output. Below is just an example which only returns the variable 'Area' and 'Perimeter' as a 1x2 matrix. I also change the variable name to 'output'.

function output = populateFields(index, structure)     
    Area(index) = getfield(structure, 'Area');
    MajorAxisLength(index) = getfield(structure, 'MajorAxisLength');
    MinoeAxisLength(index) = getfield(structure, 'MinorAxisLength');
    Eccentricity(index) = getfield(structure, 'Eccentricity');
    Orientation(index) = getfield(structure, 'Orientation');
    ConvexArea(index) = getfield(structure, 'ConvexArea');
    Circularity(index) = getfield(structure, 'Circularity');
    EquivDiameter(index) = getfield(structure, 'EquivDiameter');
    Solidity(index) = getfield(structure, 'Solidity');
    Extent(index) = getfield(structure, 'Extent');
    Perimeter(index) = getfield(structure, 'Perimeter');
    MaxFeretDiameter(index) = getfield(structure, 'MaxFeretDiameter');
    MaxFeretAngle(index) = getfield(structure, 'MaxFeretAngle');
    MinFeretDiameter(index) = getfield(structure, 'MinFeretDiameter');
    MinFeretAngle(index) = getfield(structure, 'MinFeretAngle'); 
    %
    output = [Area, Perimeter];
end 

Teshan Rezel 2021-8-12

Hi @Stephen Cobeldick, I'll try and explain the whole programme's purpose.

There are images of objects (~1500 images) which I am thresholding the background out of to get information on the shape of the object. The object colour and shape changes over the images, but also the background colour changes too. Therefore, I need to use different thresholds and techniques to get a mask for the object for different image. The idea, however, is that I have ~200 folders to threshold, each with ~1500 images, so doing this by hand isn't ideal. Hence, there are several conditions within the for loop where I switch from one threshold technique or level to another, depending on the value of the area of the thresholded object (a high difference bewteen the area of the i'th mask and the (i-1)th mask means I need to switch to the next thresholding technique). Therefore, at each image, I threshold the object/background, then measure the region properties to determine if the correct threshold has been used as well as to determine the properties of the region. I then want to store these properties into a variable. The reason I have outsourced the regionprops calls to a function is because I use the terms in the function several times during the programme.

Hope that helps.

Stephen23 2021-8-14

编辑：Stephen23 2021-8-14

在 MATLAB Online 中打开

"It seems like this technique doesn't allow for that."

Here are two simple approaches you could use. Either use the same index

for k = ..
    RG(k) = regionprops(mask1, 'all');
    RG(k).Area
    ..
end

or a temporary variable:

for k = ..
    tmp = regionprops(mask1, 'all');
    tmp.Area
    ..
    RG(k) = tmp;
end

What did you try?

Teshan Rezel 2021-8-16

在 MATLAB Online 中打开

@Stephen Cobeldick thanks for this! I tried the former, but run across this error when partway through the loop, and am not sure what's causing it...I tried defining the variable RG = zeros(numImages, 32) at the start but the error still occurs at the 465th value of i. Can I please ask you why this might be?

Unable to perform assignment because the left and right sides have a different number of elements.

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