How can I delete variables in my MAT-file without loading them into MATLAB 7.2 (R2006a)?

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MathWorks Support Team
回答： David szpliman 2018-9-19
I would like to delete variables in a MAT-file without loading them into MATLAB first.
For example, I have a file called myFile.mat which contains many variables resulting in a large MAT-file which is slow to load. I don't need all of the variables in the file.

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采纳的回答

MathWorks Support Team
MATLAB itself does not offer any functionality for deleting a particular variable from a MAT file.
 
However the MAT FILE API provides the matDeleteVariable function which allows you to delete a variable from a MAT file by its name. You can create a small MEX function in order to call matDeleteVariable. An example is attached.
 
  2 个评论
Matt J
Matt J 2017-7-28
编辑：Matt J 2017-7-28
It would also be nice to have a way of renaming variables in MAT files. Is there any API function to allow that?
Matt J
Matt J 2017-7-28
I tweaked the code to allow multiple variables to be deleted in a single call, in case anyone finds it useful.
#include "mex.h"
#include "mat.h"
/* This function removes one or more variables from a MAT file
* Compile it with
* >>mex rmvarMatfileMEX.c
* Afterwards call it with
* >> rmvarMatfileMEX(FILENAME_WITH_EXTENSION,...variables....)
* e.g.
* >> rmvarMatfileMEX('MyFile.mat','var1','var2',...)
*/
void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
MATFile *f;
char *filename;
char *vname;
int tmp;
if (nrhs >= 2 )
{
if (!mxIsChar(prhs[0]) || !mxIsChar(prhs[0]))
{
mexErrMsgIdAndTxt("RemoveVariableFromMatFile:ClassInputArguments","This function expects the inputs to be char.");
}
filename = mxArrayToString(prhs[0]);
f = matOpen(filename,"u");
if (f == NULL)
{
mxFree(filename);
mexErrMsgIdAndTxt("RemoveVariableFromMatFile:UnableToOpenFile","Could not open file. Make sure the file exists and is accessible.");
}
for (int i=1;i<nrhs;i++)
{
vname = mxArrayToString(prhs[i]);
tmp = matDeleteVariable(f,vname);
if ( tmp != 0)
{
mexWarnMsgIdAndTxt("RemoveVariableFromMatFile:UnableToDeleteVariable","Could not delete variable. Make sure that the variable exists.");
}
mxFree(vname);
vname=NULL;
}
matClose(f);
mxFree(filename);
}
}

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更多回答（1 个）

David szpliman
David szpliman 2018-9-19

Great Genius! Problem solved!

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