For Loop Table Matlab

Question

Pouyan Sadeghian 2021-5-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/838283-for-loop-table-matlab

回答： Pouyan Sadeghian 2021-6-6

采纳的回答： David Hill

在 MATLAB Online 中打开

Hey everyone,

I am working on a project and don't know how to go further.

My issue:

I have a table with measurements. I add a part of it here:

 Number              Label               MaxPosition    MinValue
    ______    __________________________    ___________    ________
       1      {'Image0100 16-28-31.bmp'}         94            0   
       2      {'Image0100 16-28-31.bmp'}        123            0   
       3      {'Image0101 16-28-46.bmp'}         95            0   
       4      {'Image0101 16-28-46.bmp'}        124            0   
       5      {'Image0102 16-29-01.bmp'}         95            0   
       6      {'Image0102 16-29-01.bmp'}        125            0   
       7      {'Image0103 16-29-16.bmp'}         96            0   
       8      {'Image0103 16-29-16.bmp'}        126            0   
       9      {'Image0104 16-29-31.bmp'}         98            0   
      10      {'Image0104 16-29-31.bmp'}        127            0   
      11      {'Image0105 16-29-46.bmp'}         98            0   
      12      {'Image0105 16-29-46.bmp'}        128            0   
      13      {'Image0106 16-30-01.bmp'}         98            0   
      14      {'Image0106 16-30-01.bmp'}        128            0   
      15      {'Image0107 16-30-16.bmp'}         99            0   
      16      {'Image0107 16-30-16.bmp'}        129            0   
      17      {'Image0108 16-30-31.bmp'}        100            0   
      18      {'Image0108 16-30-31.bmp'}        130            0   
      

In the coloumn "Label" you see the image with his index and in the column "MaxPosition" you see values.

Now I want to determine the mean value of MaxPosition for every image.

For example for the first image Image0100 the mean of the MaxPosition values -> 94+123/2 and so on.

Because I have a lot of measurements (>1000) it is impossible to calculate the mean of every image manually. I want to write a script.

I thought about to use a for loop like:

for every row in the table calculate the mean of the images with the same index or calculate the mean of the two following rows. The first case would be great but it is difficult to implement. So tried for the second case:

      for n = 1:2:height(table) % I want to write from row 1 till the last row in two steps
            mean(MaxPosition(n), MaxPosition(n+1))
      end

As you see I am a beginner and I dont know how to realize my issue.

If someone have a hint or could help me to solve my problem I would be very thankfull.

Best

P.

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Answer 1

David Hill 2021-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/838283-for-loop-table-matlab#answer_707648

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data=readtable('Results.csv');
m=mean(reshape(data.MaxPosition,2,[]));%assuming two consecutive labels for all pictures

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Pouyan Sadeghian 2021-5-24

Hey David,

sorry, of course data and not t. Thank you. I looked at help center too and didnt notice that.

Thanks.

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Answer 2

David Hill 2021-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/838283-for-loop-table-matlab#answer_707568

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m=mean(reshape(T.MaxPosition,2,[]));%assuming two consecutive labels for all pictures

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Pouyan Sadeghian 2021-5-24

编辑：Pouyan Sadeghian 2021-5-24

Hi David,

thank you for your answer.

I dont really know how to use the code because I get an error.

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Answer 3

Siddharth Bhutiya 2021-5-24

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In your case the values are consecutive so you could extract them and use mean to calculate the mean. If you did not know the number of entires for each image and the values for each image was scattered around the table then a more general approach would be to use something like varfun and use "Label" as your grouping variable and @mean as your grouping function.

t =
  10×2 table
      Label      MaxPosition
    _________    ___________
    "Image 3"        473    
    "Image 1"        418    
    "Image 2"          2    
    "Image 5"         41    
    "Image 5"         46    
    "Image 4"        467    
    "Image 5"        256    
    "Image 1"        342    
    "Image 1"        395    
    "Image 1"        123    
>> t = varfun(@mean,t,'GroupingVariables','Label')
t =
  5×3 table
      Label      GroupCount    mean_MaxPosition
    _________    __________    ________________
    "Image 1"        4               319.5     
    "Image 2"        1                   2     
    "Image 3"        1                 473     
    "Image 4"        1                 467     
    "Image 5"        3              114.33  