Replace table elements in more than one row

Question

Davindra Usov 2023-3-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1933675-replace-table-elements-in-more-than-one-row

评论： Davindra Usov 2023-3-23

Hi,

I have outputted a vector (V) which contains the row indices of elements in a table (T) that contain the string 'rpm'.

T has 3 columns and I initially set all of the elements in column 3 to zero. I now wish to replace all elements in column 3 that have these row indices (so only row 3 and row 7) with a value of 6. I have tried doing this but it doesn't work:

V = [3;7]; % row indices

for i = 1:numel(V)

T(V(i), 3) = repmat(6, numel(V), 1);

end

I get an error saying To assign to or create a variable in a table, the number of rows must match the height of the

table.

Thank you

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VBBV 2023-3-23

在 MATLAB Online 中打开

T = table(zeros(7,1),zeros(7,1),zeros(7,1),zeros(7,1))  % your table
T = 7×4 table
    Var1    Var2    Var3    Var4
    ____    ____    ____    ____

     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       0       0       0  
V = [3;7]; % row indices
T(V, 3) = [repmat({6},numel(V),1)]  % put the element in cell array when assigning
T = 7×4 table
    Var1    Var2    Var3    Var4
    ____    ____    ____    ____

     0       0       0       0  
     0       0       0       0  
     0       0       6       0  
     0       0       0       0  
     0       0       0       0  
     0       0       0       0  
     0       0       6       0  

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Answer 1

Cameron 2023-3-22

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https://ww2.mathworks.cn/matlabcentral/answers/1933675-replace-table-elements-in-more-than-one-row#answer_1198760

在 MATLAB Online 中打开

You should look into how MATLAB does its indexing. You don't have to loop through the array to change a value. Just do it like this:

T = zeros(10,3); %i just picked 10 rows of data
indx = [3,7];
T(indx,3) = 6
T = 10×3
   0     0
   0     0
   0     6
   0     0
   0     0
   0     0
   0     6
   0     0
   0     0
   0     0

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Davindra Usov 2023-3-23

thank you very much. This works perfectly. The others do as well, however I can only accept one answer

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Answer 2

Cris LaPierre 2023-3-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1933675-replace-table-elements-in-more-than-one-row#answer_1198770

编辑：Cris LaPierre 2023-3-22

在 MATLAB Online 中打开

You can, but the code you wrote is trying to replace a single element with a vector, hence the error message.

When you are trying to replace each element with the same value, you do not need to use repmat. Perhaps you are trying to do this?

tb = table(zeros(4,1))
tb = 4×1 table
    Var1
    ____

     0  
     0  
     0  
     0  
tb.Var1([1 3]) = 6
tb = 4×1 table
    Var1
    ____

     6  
     0  
     6  
     0  
% you could also use repmat if you want
tb.Var1([2 4]) = repmat(10,2,1)
tb = 4×1 table
    Var1
    ____

      6 
     10 
      6 
     10 