How to create a Matrice from a structure

Hello everyone, first sorry for my poor english ^^

I ask for your help today because I have a little problem.

I have created a structure like this :

values=regionprops(L,image,'PixelValues')

So, here I have a structure named 'values' that contains intensity values for each pixel of each 'region' or 'object' L. Some region contains 5 pixels, some others only 1 so and so..

So I have a structure like this, for exemple: values

ans= 150
     200
ans= 125
     75
     21
ans= 50

etc etc

I want to create a matrice with this structure and I dont know how to do it.

In my program I have already created a matrice from a structure. My structure is

   meanValues=regionprops(L,image,'MeanIntesity')

and so,

matrice=cell2mat(struc2cell(meanValues))

and it works well.

Why does it work for this one ? Because meanValues is a structure that contains only one value for each region. So there are any probleme to create a matrice from this.

How can I create a matrice for my strucuture named 'values' ?? I don't know..

Thanks for reading, and for youre future answers :) !

[Rakesh Chavan]

Hi,

Please correct me if my understanding of your question is wrong.

In the first case you have a variable sized arrays in your structure which can be converted to a cell but not to a matrix.

In the second case I think you only have fixed number of values in the structure which is why you are able to create a matrix.

For example:

s = 

      a: 1
      b: 2
      c: 2

>> cell2mat(struct2cell(s))

ans =

       1
       2
       2

Whereas

s = 

      a: 1
      b: 2
      c: [2 9]

>> cell2mat(struct2cell(s))

Gives an error.

A sample script may be helpful in explaining the problem you are facing. This may assist others in providing a resolution to the query.

Hope this helps

-

Rakesh

[Hidir ABAY]

Hello, thank you for your answer and your advice.

Answer 1

[Guillaume]

"...and it works well." and is also overly complicated:

meanintensity = [meanValues.meanIntensity];

will be a lot faster and is the proper way to convert scalar fields of a structure array into a matrix.

The answer to your question depends on which fields of the regionprops structure you want to convert to a matrix. Unfortunately, you haven't told us that. However, if as you say it's one of these fields with a various number of element, how are you expecting to have that into a single matrix?

Maybe you want to concatenate it all into one vector:

allPixelIdxList = vertcat(values.PixelIdxList);

Note that the above will only work if the field you want to concatenate is always a column vector.

But in the end, why do you want to convert the output into a matrix? Why can't you work with the structure as it is?

[Hidir ABAY]

Hello, haha you were right, I did not need to work with matrix. I find the way to use my structure. Thanks for your answer.

Answer 2

[Nut]

Hi,

if "meanValues" is a single value and you return a 2d matrix from it, I think that if "values" is an array you should return a 3d matrix. I don't know the right command to do this... but if you can accept a not much efficient solution, you can try to apply the same syntax you have already created. Example (this is not a right syntax, it is just to explain the solution, you have to adjust it):

 matrice = zeros(dim1,dim2,number_of_values); % Preallocation of "matrice"

 for i = 1:number_of_values

 matrice(:,:,i) = matrice=cell2mat(struc2cell(values(i)))

 end

[Hidir ABAY]

Thank you for your answer I hope it will help another one. I find a way to work with my structure and so I don't need to create a matrix anymore. Have a nice day.