Use forLoop to manipulate values of elements in a specific column

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JZ 2015-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/258958-use-forloop-to-manipulate-values-of-elements-in-a-specific-column

评论： lsutiger1 2015-12-6

采纳的回答： Star Strider

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I created the following 5x5 matrix with no data:

mat = zeros(5:5)
mat =
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0

I would like to use a for loop to generate the following result

mat =
       0     0     0     0      0
       0     0     0     10     0
       0     0     0     20     0
       0     0     0     30     0
       0     0     0     40     0

I attempted using the following code, but the operation was performed on the first column - not the 4th, as I had intended.

for i = 2:length(mat(:,4))
mat(i) = mat(i-1) + 10;
end

This was the actual result

mat =
       0     0     0     0     0
      10     0     0     0     0
      20     0     0     0     0
      30     0     0     0     0
      40     0     0     0     0

I imagine this is a simple syntax problem, but I am not finding the solution in any of the forums. Any help is appreciated.

Thanks

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Star Strider 2015-12-5

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This works:

mat = zeros(5:5);
mat(:,4) = 0:10:10*(size(mat,1)-1);
mat =
     0     0     0     0     0
     0     0     0    10     0
     0     0     0    20     0
     0     0     0    30     0
     0     0     0    40     0

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JZ 2015-12-5

编辑：JZ 2015-12-5

That is indeed a much simpler solution - thank you!

And thanks for the clarification on cell/element. No offense taken.

Star Strider 2015-12-5

My pleasure!

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lsutiger1 2015-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/258958-use-forloop-to-manipulate-values-of-elements-in-a-specific-column#answer_202259

You have only specified the row that you want to manipulate; you need to specify both the row and column.

mat(i) = mat(i-1,4) + 10;

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JZ 2015-12-5

在 MATLAB Online 中打开

Thanks, but I am still getting errors with both of your suggestions:

mat = zeros(5:5)
mat =
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0
       0     0     0     0     0
mat(i,4) = mat(i-4,4) + 10;
Index exceeds matrix dimensions.
mat(i) = mat(i-1,4) + 10;
Index exceeds matrix dimensions.