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Add new data into existing mat file

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Hazel Sialongo 2016-9-28

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评论： Stephen23 2021-8-25

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How to add new data in the existing mat file?

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Stephen23 2016-9-28

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在 MATLAB Online 中打开

The save documentation gives this syntax:

save(filename,variables,'-append')

and describes it as " save(filename,variables,'-append') adds new variables to an existing file. If a variable already exists in a MAT-file, then save overwrites it. The variables argument is optional."

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Hazel Sialongo 2016-9-28

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I want to add data not to overwrite the data.

Stephen23 2016-9-28

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编辑：Stephen23 2016-9-28

在 MATLAB Online 中打开

"I want to add data not to overwrite the data."

Lets read the line from the documentation more carefully then: "adds new variables to an existing file"

Here is an example of using the -append option, exactly like my answer states:

>> X = 1:3;
>> Y = 4:6;
>> save('test','X','Y')
>> Z = 7:9;
>> save('test','Z','-append')
>> S = load('test.mat')
S = 
    X: [1 2 3]
    Y: [4 5 6]
    Z: [7 8 9]

So the answer that I gave you worked perfectly: it appended the new data without overwriting anything. Did you actually try it? Does this do what you want?

If you want to append data to an array in the mat file then the easiest way is to use matfile, which lets you "Access and change variables directly in MAT-files, without loading into memory", as is explained here:

http://blogs.mathworks.com/loren/2011/10/14/new-mat-file-functionality-in-r2011b/

Hazel Sialongo 2016-9-28

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But the data is from the gui edit toolbox.

blues 2019-10-23

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Hi Stephen,

What if I want to add a data to the existing variables X and Y in your example? Let's say, I want to add X = 10:15; and Y = 20:25; in the test.mat file, how can I do this?

Stephen23 2019-10-24

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@blues : either:

load, concatenate, save, or
use matfile.

If using option 1. remember to load into an output variable rather than directly into the workspace.

blues 2019-10-24

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Hi Stephen,

Could you give me suggestion on the following example?

I have a data in the following format: (i, j, k, val) where i, j, k are variables and val is the corresponding data at i, j, k values. I want to save the .mat file in the (i, j, k, val) format, so that my .mat files looks like:

(0, 0, 0, 1.5E-02)

(0, 0, 1, 2.5E-05)

...........................

(5, 5, 5, 4.5 E-05)

How can I create this type of .mat file?

Actually these data are the octant of a 11 by 11 by 11 matrix (isotropic cubic matrix). I would like to have a full-size matrix using the symmetry property of the octant. I want to save the octant data in a .mat file so that I could iterate over the 8 possibilities to make a full size matrix.