Loading files by replacing some part of the name with a variable

Hi, I want to load a bunch of files in my workspace. There all name simmilarly and there's a number counting up, but its not just at the end of the Filename, so just replacing it with 'i' doesn't work.

Any ideas?

The 'i' in the file name are two digits. Starting with '01' and ending with '41'

I found a Video of someone explaining a similar issue, but I wasn't able to adapt the solution to my code.

for i = 01:41
FileName   = 'GNSS_Validierung_0i.mat';
FolderName = 'C:\Users\Admin\Documents\BA\MATLAB\Routenplanung\versuchsdaten_maxi';
File       = fullfile(FolderName, FileName);
load(File);   


x_DIY_flip = GNSS_Validierung_0i.Y(23).Data';
y_DIY_flip = GNSS_Validierung_0i.Y(25).Data';

x_ppm_flip = GNSS_Validierung_0i.Y(24).Data';
y_ppm_flip = GNSS_Validierung_0i.Y(26).Data';
.
.
.
end

[Stephen23]

The MATLAB documentation shows you one approach using SPRINTF:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

And then remember to always LOAD into an output variable:

S = load(..);

and then access its fields. Then you can avoid that major problem with magical dynamic variable names.

[Dyuman Joshi]

Have a look at this - https://in.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

How do you get the data i.e. all the mat file, in the manner (using numbers in the name i.e. dynamically naming them) you have now? Is the data output from some code?

Answer 1

[Matt J]

Pre-generate all of the filenames and loop over them.

FileNames   = compose("GNSS_Validierung_%.2d",(1:41)' )

FileNames = 41×1 string array
    "GNSS_Validierung_01"
    "GNSS_Validierung_02"
    "GNSS_Validierung_03"
    "GNSS_Validierung_04"
    "GNSS_Validierung_05"
    "GNSS_Validierung_06"
    "GNSS_Validierung_07"
    "GNSS_Validierung_08"
    "GNSS_Validierung_09"
    "GNSS_Validierung_10"
    "GNSS_Validierung_11"
    "GNSS_Validierung_12"
    "GNSS_Validierung_13"
    "GNSS_Validierung_14"
    "GNSS_Validierung_15"
    "GNSS_Validierung_16"
    "GNSS_Validierung_17"
    "GNSS_Validierung_18"
    "GNSS_Validierung_19"
    "GNSS_Validierung_20"
    "GNSS_Validierung_21"
    "GNSS_Validierung_22"
    "GNSS_Validierung_23"
    "GNSS_Validierung_24"
    "GNSS_Validierung_25"
    "GNSS_Validierung_26"
    "GNSS_Validierung_27"
    "GNSS_Validierung_28"
    "GNSS_Validierung_29"
    "GNSS_Validierung_30"

[Simon Schirk]

Thans, that solves the Problem with the loading of the files, but I use the file name through the program moreoften, so I still need to modify alle the Paths where I want to use some Data out of the file.

[Matt J]

You need to call load with an output argument

S=load(FileNames{i}).(FileNames{i});

Then, you can access the data by doing things like,

x_DIY_flip = S.Y(23).Data';

[Stephen23]

"you can access the data by doing things like"

Not quite, because the first nested structure will be e.g. GNSS_Validierung_01, under which Y can be found.

[Matt J]

Not quite, because the first nested structure will be e.g. GNSS_Validierung_01, under which Y can be found.

The dot-indexed manner in which I called the load() command should take care of that.

[Stephen23]

@Matt J: ah, I missed that dot indexing. Note that ".mat" is not valid in fieldnames.

[Matt J]

@Stephen23 Good point. I've removed the .mat sub-string from the code I proposed (it was never necessary).

Answer 2

[Stephen23]

Do NOT name each variable dynamically. Unless you want to force yourself into writing slow, complex, inefficient, insecure, obfuscated code that is buggy and hard to debug.

Always LOAD into an output variable (which is a scalar structure). The your data-access problems are easily avoided:

P = 'C:\Users\Admin\Documents\BA\MATLAB\Routenplanung\versuchsdaten_maxi';
for k = 01:41
    F = sprintf('GNSS_Validierung_%02d.mat',k);
    C = struct2cell(load(fullfile(P,F));
    assert(isscalar(C),'Exactly one variable is allowed!')
    x_DIY_flip = C{1}.Y(23).Data.';
    y_DIY_flip = C{1}.Y(25).Data.';
    x_ppm_flip = C{1}.Y(24).Data.';
    y_ppm_flip = C{1}.Y(26).Data.';
    .
    .
    .
end

Note that your code would be simpler, more efficient, and much more robust if the variable names were exactly the same in every MAT file. That is to say, the data you have been given is badly designed.