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

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qmnjb007
qmnjb007 2018-1-11
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

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Matt J
Matt J 2018-1-11
编辑：Matt J 2018-1-11
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) );
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Matt J
Matt J 2018-1-11
编辑：Matt J 2018-1-11
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
qmnjb007
qmnjb007 2018-1-11
Thanks Matt and Steven; loading the data in the main script and then passing the structure to the functions was the solution I was looking for!

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