How can I plot a histogram for each of the multiple .mat files located in a folder outside of MATLAB?

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bobby 2021-9-29

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评论： bobby 2021-9-29

I am new to using MATLAB to analyze and visualize many individual files of data.

Here is the situation: I have multiple (20+ but can certainly extend to the 50-60+ range) .mat files that are typically (but not always) in the form of a 1024x1024 matrix. These .mat files are automatically placed in a folder outside of MATLAB (the folder's location is specified as the save file path in a seperate script). Each of those codes share a common naming tag (ie. an identifying text that can be used to readily identify the targeted .mat files).

I would like to be able to produce a reusable code that can take all of the selected .mat files in that filepath and produce a histogram for each .mat at the same time. The values of the matricies can differ so I wouldn't want to put any restraints on axises or rows/columns.

The code I have so far is as follows:

clear all
%The Code below specifies the filepath on my computer where said .mat files are located in
directory = '/Users/NAME/Desktop/selectedmatricies/';
realdata = dir(directory);
%MATLAB Version: 9.7.0.1261785 (R2019b) Update 3

I am unsure where to go from here, or even if the code I listed above is even needed for what I am intending. I do have some suspiscion that a for loop would play a role in the code that would be generated, but I do not know how to structure it.

I have scoured MathWorks for previously asked questions in a similiar predicament to mine, however my efforts were fruitless. I am very much open to any ideas or codes that the community can provide! Thank you so much everyone!

TLDR; I would like to take multiple .mat files in an outside folder and run them through MATLAB code to produce a histogram per file

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Answer 1

Kevin Holly 2021-9-29

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编辑：Kevin Holly 2021-9-29

在 MATLAB Online 中打开

Here is one method you can use:

directory = '/Users/NAME/Desktop/selectedmatricies/'; %Alternatively, could use: directory = uigetdir()
files=dir(fullfile(directory,'*.mat')); % This gets all the .mat files in the directory. * is a wild card
save_directory=uigetdir('C:\'); % Where you want to save your histograms
%let's analyze each file
for i = 1:length(files)
    matrix = load([file(i).folder,filesep,file(i).name],'-mat');
    histogram(matrix)
    xlabel('X label')
    ylabel('Y label')
    title('title')
    saveas(gcf,[save_directory,filesep,strrep(file(i).name,'.mat','.fig')],'fig'); %save figure (can also save as an image (e.g. .png or .tif))
    % Could use the line below if you want to save the figure with the word histogram
    %saveas(gcf,[save_directory,filesep,strrep(file(i).name,'.mat','_histogram.fig')],'fig'); %save figure
end

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Kevin Holly 2021-9-29

编辑：Kevin Holly 2021-9-29

在 MATLAB Online 中打开

I made a few changes:

directory = '/Users/NAME/Desktop/selectedmatricies/'; %Alternatively, could use: directory = uigetdir()
files=dir(fullfile(directory,'*.mat')); % This gets all the .mat files in the directory. * is a wild card
uiwait(msgbox('Please select the folder in which you want to save the histogram files'))
save_directory=uigetdir('C:\'); % Where you want to save your histograms
%let's analyze each file
for i = 1:length(files)
    Data = load([files(i).folder,filesep,files(i).name],'-mat');
    histogram(Data.matrix) %Note "matrix" needs to be replaced with the variable you want to load in the .mat file.
    xlabel('X label')
    ylabel('Y label')
    title('title')
    saveas(gcf,[save_directory,filesep,strrep(files(i).name,'.mat','.fig')],'fig'); %save figure (can also save as an image (e.g. .png or .tif))
    % gcf stands for get current figure. strrep() is a string replace
    % function. I replaced '.mat' with '.fig' in this case.
    % Could use the line below if you want to save the figure with the word histogram
    %saveas(gcf,[save_directory,filesep,strrep(file(i).name,'.mat','_histogram.fig')],'fig'); %save figure
end

I added a step, so you can choose where you want to save your histograms. See comments in the code. I added a message box for clarity.

bobby 2021-9-29

在 MATLAB Online 中打开

Doing it Kevin Holly's way, the code is listed below. Running that exact code, I get an error that is as shown:

Reference to non-existent field 'matrix'.

Error in histogramFunction (line 16)

histogram(Data.matrix)

for i = 1:length(files)
    
    Data = load([files(i).folder,filesep,files(i).name],'-mat')
    histogram(Data.matrix) %this is wear the error occurs aka line 16
    xlabel('X label')
    ylabel('Y label')
    title('title')
    
    %gcf stands for get current figure. strrep() is a string replace
    saveas(gcf,[save_directory,filesep,strrep(files(i).name,'.mat','.fig')],'fig'); %save figure (can also save as an image (e.g. .png or .tif))
end

Doing it Image Analyst's way, the code is listed below. Running that exact code, I get an error that is as shown:

Unrecognized function or variable 'file'.

Error in histogramFunction (line 14)

matrix = load(fullfile(file(i).folder, file(i).name))

for i = 1:length(files)
    
    matrix = load(fullfile(file(i).folder, file(i).name))
    histogram(Data.matrix)
    xlabel('X label')
    ylabel('Y label')
    title('title')
    
    %gcf stands for get current figure. strrep() is a string replace
    saveas(gcf,[save_directory,filesep,strrep(files(i).name,'.mat','.fig')],'fig'); %save figure (can also save as an image (e.g. .png or .tif))
end

Image Analyst 2021-9-29

在 MATLAB Online 中打开

I'd just add

drawnow;

after histogram() to make sure it paints the screen every time. Otherwise you might just see the latest histogram only.

bobby 2021-9-29

@Kevin Holly and @Image Analyst, thank you for sticking with me through this issue and lending your expert suggestions! From your guidance and expertise, I was able to figure out the code that would be able to work with my current script! Thank you both so very much!

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Answer 2

Image Analyst 2021-9-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1462859-how-can-i-plot-a-histogram-for-each-of-the-multiple-mat-files-located-in-a-folder-outside-of-matlab#answer_797754

The answer to this and lots of other good stuff can be found in the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

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bobby 2021-9-29

Thank you! I see that the first example would be most relevant but how would I change that code to analyze .mat files into histograms, rather than it analyzing a group of .png files as seen in the example? Would the code still be the same?

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How can I plot a histogram for each of the multiple .mat files located in a folder outside of MATLAB?

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How can I plot a histogram for each of the multiple .mat files located in a folder outside of MATLAB?

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