How to deal with the structure?

Question

Benson Gou 2021-6-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/867503-how-to-deal-with-the-structure

评论： Benson Gou 2021-7-7

采纳的回答： Jan

在 MATLAB Online 中打开

Dear All,

I have a struct which saves a number of records. I have the following codes which takes more time than expected.

Resstd2 = [];
resstd20 = [];
treestruct2 = [];
nnzV = find(v);
m1 = length(TreeStruct2);
temp = [];
for i = 1 : m1
    vblockid = TreeStruct2(i).treestruct.vblockID;
    solvedvid = v(vblockid);
    resstd2 = TreeStruct2(i).Resstd;
    if nnz(solvedvid) == 0
        if resstd2(3) < voltagelimit
            treestruct2 = [treestruct2; TreeStruct2(i).treestruct];
            Resstd2 = [Resstd2; resstd2];
        else
            resstd20 = [resstd20; resstd2];
        end
    end
    temp = [temp; resstd2(3)];
end

It seems to me that using structures takes long time. Does anyone have the experience in cell or table? Do you think using cells or tables will be faster than using structures?

Thanks.

Benson

3 个评论
显示 1更早的评论隐藏 1更早的评论

Rik 2021-6-30

在 MATLAB Online 中打开

Your edit doesn't seem to address the issue I raised in my comment. Without a good description of what you want, the only thing we can say is not to use a dynamic expansion.

If you want help with your code specifically, you should make sure we can run it.

Resstd2 = [];
resstd20 = [];
treestruct2 = [];
nnzV = find(v);
Unrecognized function or variable 'v'.

Benson Gou 2021-6-30

Hi, Rik,

Thanks a lot for your reply.

The data is big and is hard to display the data in my question. Is it possible to attached the mat file in my question?

Thanks.

Benson

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2021-6-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/867503-how-to-deal-with-the-structure#answer_736803

编辑：Jan 2021-6-30

在 MATLAB Online 中打开

Do not let arrays grow iteratively because this causes exponentially growing computing times. Example:

x = [];
for k = 1:1e6
   x(k) = k;
end

Although the final array has only 8MB (8 bytes per double), Matlab has to allocate a new array in each iteration and copy the old values. In total this allocates sum(1:1e6)*8 = 4TB!

m1          = length(TreeStruct2);
Resstd2     = zeros(m1, 1);
Resstd2_i   = 0;
resstd20    = zeros(m1, 1);
resstd20_i  = 0;
treestruct2_m = false(m1, 1);
% nnzV = find(v);  % Not used
temp = zeros(m1, 1);
for i = 1 : m1
    vblockid  = TreeStruct2(i).treestruct.vblockID;
    solvedvid = v(vblockid);
    resstd2   = TreeStruct2(i).Resstd;
    if ~any(solvedvid)   % Faster than nnz==0
        if resstd2(3) < voltagelimit
            treestruct2_m = true;
            Resstd2_i     = Resstd2_i + 1;
            Resstd2(Resstd2_i) = resstd2;
        else
            resstd20_i  = resstd20_i + 1;
            resstd20(resstd20_i) = resstd2;
        end
    end
    
    temp(i) = resstd2(3);
end
Resstd2  = Resstd2(1:Resstd2_i);    % Crop unused elements
resstd20 = resstd20(1:resstd20_i);  % Crop unused elements
treestruct2 = cat(1, TreeStruct2(treestruct2_m).treestruct);

Maybe Resstd2 and resstd20 need more dimension. Without provided input data, e.g. created by RAND() I cannot guess this. Adjust the dimensions on demand.