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How to use If elseif else in array ?

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Ajaree Rattanaharn
Ajaree Rattanaharn on 6 Feb 2019
Commented: YT on 7 Feb 2019
I have variables of the image call 'IGray' in picture below
variables IGray.png
now I want to write the if elseif code to find amount of the value that I separate in 3 ways
  1. the value < 50
  2. the value 50-220
  3. 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 ^^
Steven Lord
Steven Lord on 6 Feb 2019
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
Ajaree Rattanaharn on 7 Feb 2019
Yess I try but I can't write the code

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Accepted Answer

YT on 6 Feb 2019
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.
% dummy matrix
A = randi([0 255],1171,1591);
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;
ThW1 = ThW1 + 1;
% Elapsed time is 0.055028 seconds.
% alternative logical indexing (...but this is brilliant)
ThB2 = sum((A <= 50),'all');
ThBW2 = sum(((A > 50) & (A <= 220)),'all');
ThW2 = sum((A > 220),'all');
% Elapsed time is 0.003860 seconds.
Stephen23 on 7 Feb 2019
Edited: Stephen23 on 7 Feb 2019
@Ajaree Rattanaharn: The vector dimension / 'all' option was added in R2018b:
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 on 7 Feb 2019
Like @Stephen Cobeldick suggested, instead of using 'all', you can try this instead
sum(sum(((A > 50) & (A <= 220)),1),2)

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