Does loading a table in a subfunction I'm calling slow my routine down?

Question

qmnjb007 2018-1-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376740-does-loading-a-table-in-a-subfunction-i-m-calling-slow-my-routine-down

评论： qmnjb007 2018-1-11

I have a script which contains a function that calls a sub-function many times, where the sub-function analyzes data from a large, read-only 8000 x 5 table that never changes. I load the table at the beginning of the sub-function. Question: am I slowing down my script dramatically by re-loading the same data each time I call the sub function? Is there a better way to do this? Simplified code below:

**********myfun.m********************

function tt = myfun(z)
i = 1;
sum_one = 0;
sum_two = 0;
for i = 1:z;
     t = mysubfun(i);
     sum_one = sum_one + t(1,1)
     sum_two = sum_two + t(1,2)
   end
tt = table(sum_one, sum_two)
end

***********mysubfun.m*******************

function  t = mysubfun(x)
      load('data.mat') %loads a table that is 8000 x 5
      t = table(sum(data(1:x,1),sum(data(1:x,2))
  end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Matt J 2018-1-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376740-does-loading-a-table-in-a-subfunction-i-m-calling-slow-my-routine-down#answer_299734

编辑：Matt J 2018-1-11

在 MATLAB Online 中打开

Yes, you are dramatically slowing things down.

I can't be sure what your code is trying to do (it would produce error messages as you've written it), but I don't think you need the sub-function or even the loop. I think it can all be done in two lines as follows,

load('data.mat')
tt=array2table(  cumsum(data(:,1:2),1)   );

6 个评论
显示 4更早的评论隐藏 4更早的评论

Matt J 2018-1-11

编辑：Matt J 2018-1-11

在 MATLAB Online 中打开

That really is not a good idea, for one thing because global variables cannot be made read-only. You should probably just pass data around as a regular function input argument as below.

    function tt = myfun(z)
              S=load('data.mat') %loads a table that is 8000 x 5
              data=S.data; clear S
              i = 1;
              sum_one = 0;
              sum_two = 0;
              for i = 1:z;
                   t = mysubfun(i,data);
                   sum_one = sum_one + t(1,1);
                   sum_two = sum_two + t(1,2);
                 end
              tt = table(sum_one, sum_two);
    end
     function out = mysubfun(x,data)
          out = table(   sum(data(1:x,1))  ,  sum(data(1:x,2)) );
     end

However, if for some reason this is too cumbersome, the next best thing would be to make the data a Constant property of a class

 classdef readOnly %put in a file called readOnly.m
   properties (Constant)
      data=getfield(load('data.mat'),  'data');
   end
 end

Now, any function anywhere can access the data, like in the following

    function tt = myfun(z)
              i = 1;
              sum_one = 0;
              sum_two = 0;
              for i = 1:z;
                   t = mysubfun(i);
                   sum_one = sum_one + t(1,1);
                   sum_two = sum_two + t(1,2);
                 end
              tt = table(sum_one, sum_two);
    end
     function out = mysubfun(x)
          out = table(   sum(readOnly.data(1:x,1))  ,...
                         sum(readOnly.data(1:x,2)) );
     end