How to use If elseif else in array ?

Question

Ajaree Rattanaharn 2019-2-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/443498-how-to-use-if-elseif-else-in-array

评论： YT 2019-2-7

采纳的回答： YT

I have variables of the image call 'IGray' in picture below

now I want to write the if elseif code to find amount of the value that I separate in 3 ways

the value < 50
the value 50-220
the value > 220

primary, I try to write but it can not . As shown below

which I want ThW, ThWB and ThB show in the workspaces and it can double click to show all variables.

Please help me TT

Thank you very much ^^

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Steven Lord 2019-2-6

Do you want to display ThW in the Command Window once if any of the elements in Threshold_IGray is greater than or equal to 220, once if all the elements in Threshold_IGray is greater than or equal to 220, or a number of times equal to the number of elements in Threshold_IGray that are greater than or equal to 220? You're likely to get a different number of ThW's displayed in each of those three scenarios.

Ajaree Rattanaharn 2019-2-7

Yess I try but I can't write the code

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Answer 1

YT 2019-2-6

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/443498-how-to-use-if-elseif-else-in-array#answer_359745

So everytime I have to do somethings similar, I either do it by using a for-loop and if/else statement and comparing every field of the matrix (ii,jj) to the condition OR I use logical indexing. So I've provided both options to show you the difference in the amount of code and the execution time.

clear;
%  dummy matrix
A = randi([0 255],1171,1591);
tic
ThB1 = 0;
ThBW1 = 0;
ThW1 = 0;
% with for-loop and if/else (I like this...)
for ii = 1:size(A,1)
   for jj = 1:size(A,2)
      if(A(ii,jj) <= 50)
          ThB1 = ThB1 + 1;
      elseif(((A(ii,jj) > 50) && (A(ii,jj) <= 220)))
          ThBW1 = ThBW1 + 1;
      else
          ThW1 = ThW1 + 1;
      end
   end
end
toc
% Elapsed time is 0.055028 seconds.
tic
% alternative logical indexing (...but this is brilliant)
ThB2 = sum((A <= 50),'all');
ThBW2 = sum(((A > 50) & (A <= 220)),'all');
ThW2 = sum((A > 220),'all');
toc 
% Elapsed time is 0.003860 seconds.

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Stephen23 2019-2-7

编辑：Stephen23 2019-2-7

@Ajaree Rattanaharn: The vector dimension / 'all' option was added in R2018b:

https://www.mathworks.com/help/matlab/release-notes.html?rntext=sum+all&startrelease=R2018a&endrelease=R2018b&groupby=release&sortby=descending&searchHighlight=sum+all

For earlier versions you will have to either use (:), or used nested sum calls.

Note that you should always look at the documentation for your installed MATLAB version, which would have made it clear that it does not support this option.

YT 2019-2-7