How can I remove a variable from the parent workspace while a function is using it?

Question

Sean 2011-12-14

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I work with fairly large datasets, so the fact that they get duplicated when a function accepts them as an input can be a problem given 32bit memory constraints.

I have started using scripts instead of functions in order to save on memory usage, but this has caused additional problems, because now their is no distinction between the workspaces and I have to be very careful not to overwrite utility variables (such as x, y, t, n, etc.)

I would really like to pass a variable as a function input such that there are not two copies floating around the system.

How can I remove the variable from the parent workspace (or possibly act directly on only the parent workspace variables that are specified as functional inputs?)

Thanks, Sean

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Answer 1

the cyclist 2011-12-14

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Are you changing the value of the variable after it is passed in? If not, then a copy is never made.

If it is changed, you could define the variable as global to ensure having only one copy.

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Sean 2011-12-14

I have a natural aversion to using global variables, because it is so easy to cause problems that way, but perhaps this is one of the few 'correct' times to use a global...

The reason I am not using nested functions is because I do not want to risk overwriting other variables in the parent workspace.

Walter Roberson 2011-12-14

The only variables that can be overwritten are the ones that are initialized before the nested routines are declared.

function parent

shared1=[];

function nested1

shared1='hello'; %affects shared variable

i=15; %local variable because it was not initialized before nested routine

end

i=32; %local variable because it was not initialized before nested routine

nested1(); %will affect shared1 but not i

end

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Answer 2

Walter Roberson 2011-12-14

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https://ww2.mathworks.cn/matlabcentral/answers/23968-how-can-i-remove-a-variable-from-the-parent-workspace-while-a-function-is-using-it#answer_31451

在 MATLAB Online 中打开

To answer the original question:

evalin('caller', ['clear ', inputname(3)])

where the 3 here should be changed to the parameter number of the variable in the calling sequence.

Crashes due to doing this would not surprise me.

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Sean 2011-12-14

Walter,

Thanks for the answer. I was unfamiliar with the 'evalin' command. I can see that it would work for what I was asking, but can also potentially be badly abused. :)

I would mark you as the accepted answer, but I already marked 'the cyclist' as such.

Thanks again,

Sean

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