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Appending multiple variables onto a single file

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Hey all! So I'm having a bit of an issue in saving variables onto a single file. I have a variable called 'map' which is the result of a piece of code that I run for one single file at a time. I want to combine all the 'map' variables for all the files that I'm using to give me an image as the final result. The input for the final result is as follows
figure; imagesc(mean(map,3)); axis image; colormap(1-gray(256))
What is the best way to combine one map variable from one file with another map variable from another file, so that I can get a combined image for the figure. Saving the variables to a single .mat file just seems to overwrite the previous 'map' variable. Thanks in advance! Also the 'map' variable is a 1069X1900 double.

Accepted Answer

Walter Roberson
Walter Roberson on 14 May 2021
dinfo = dir('*.mat');
filenames = {};
nfile = length(filenames);
hasmap = false(nfile,1);
for K = 1 : nfile
info = whos('-file', filenames{K}, 'map');
if ~isempty(info)
hasmap(K) = true;
filenames = filenames(hasmap);
nfiles = length(filenames);
allmap = [];
for K = 1 : nfiles
datastruct = load(filenames{K}, 'map');
thisdata =;
if K == 1
alldata = thisdata;
if nfiles > 1
alldata(end,end,nfiles) = 0;
alldata(:,:,K) = thisdata;
This code does not assume a particular size for the map variable, but it does assume that all of the map variables are the same size.
This code does not assume that all .mat files in the directory contain a map variable.
The purpose of the loop with whos is optimization: the code locates files that have the map variable and selects only those files, which gives you the count of files. Then when the first file is read in, the code takes the array of data and zero pads it out to the final size. This saves MATLAB from having to extend the array dynamically.
There are other ways of achieving the same efficiency.

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