Accessing elements in a structure

I have 2 matlab files, both containing 2 elements: velocity and points.

i have loaded these two files into a structure, but now I want to access each individual field in the velocity column and do some calculations in it (e.g. work out the mean value).

I am struggling to access each field, could anybody help me please?

file = dir('*.mat'); 
num_files = length(file); 
[~, index] = natsort({file.name}); 
filelist = file(index);
out = load(filelist(1).name);
for k = 1:numel(filelist)
    out(k) = load(filelist(k).name); 
end

[Stephen23]

Unless you have a good reason for using NATSORT you should probably use NATSORTFILES:

https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

which lets you write simpler code by directly sorting the output from DIR:

P = 'absolute or relative filepath to where the files are saved';
S = dir(fullfile(P,'*.mat'));
S = natsortfiles(S); % <------- much simpler!
for k = 1:numel(S)
    F = fullfile(P,S(k).name)
    ... etc
end

Answer 1

[KSSV]

file = dir('*.mat'); %fine all the .mat files
num_files = length(file); %record how many files have been found
[~, index] = natsort({file.name}); %sort the files into order
filelist = file(index);
GTav = zeros(numel(filelist),1)
for k = 1:numel(filelist)
    load(filelist(k).name); % I hope the structure is named out in every file           
    % For each cell in the velocity column of the structure
    v1 = vel ;
    %1. calculate the resultant velocity of each particle
    ResV = sqrt((v1(:,1).^2) + (v1(:,2).^2) + (v1(:,3).^2));
    %2. calculte the mean resultant velocity of all the particles
    ResVav = mean(ResV);
    %3. calculate the granular temperature of all the particles
    GT = ResV-ResVav;
    %4. calculate the average granular temperature for each field
    GTav(k) = mean(GT);
end

[C.G.]

Thank you for your response.

I understand what you have done here, but I want to eventually use this to process 1 million files. I am just trying to set-up the code to process this. Is there a way to access these without having to set up 1 million variables?

[KSSV]

file = dir('*.mat'); 
num_files = length(file); 
[~, index] = natsort({file.name}); 
filelist = file(index);
out = cell
for k = 1:numel(filelist)
    load(filelist(k).name); 
    p1 = out(1).points ;v1 = out(1).vel ;
    p2 = out(2).points ;v2 = out(2).vel ;
    % do what you want and save 
end

[C.G.]

even still wont I then have to write p1 and v1 out to 1 million?

[KSSV]

If you keep on appending the data wont memory exceed? If you want all of them in an array use:

file = dir('*.mat'); 
num_files = length(file); 
[~, index] = natsort({file.name}); 
filelist = file(index);
out(numel(filelist)) = struct ; 
for k = 1:numel(filelist)
    out(k).data = load(filelist(k).name);        
end

[C.G.]

I cant change the amount of files I have. Here I write the full code of what I wish to do to each field in the velocity column. But I need this for each field in the velocity column if I have multiple files to load in and not just the one. All I need to save from this is the GTav for each field.

file = dir('*.mat'); %fine all the .mat files
num_files = length(file); %record how many files have been found
[~, index] = natsort({file.name}); %sort the files into order
filelist = file(index);
out = load(filelist(1).name); %pre-assign a structure for the data to go into
for k = 1:numel(filelist)
    out(k) = load(filelist(k).name); %load the files into the structure 
end

% For each cell in the velocity column of the structure
v1 = out(1).vel ;
%1. calculate the resultant velocity of each particle
ResV = sqrt((v1(:,1).^2) + (v1(:,2).^2) + (v1(:,3).^2));
%2. calculte the mean resultant velocity of all the particles
ResVav = mean(ResV);
%3. calculate the granular temperature of all the particles
GT = ResV-ResVav;
%4. calculate the average granular temperature for each field
GTav = mean(GT);

[KSSV]

Edited the main answer.

[C.G.]

thank you. When you say 'I hope the structure is named out in every file', all my files are named out_1.mat, out_2.mat etc.

but I am getting the following error: Undefined variable "out" or class "out.vel". I have attached my 3 .mat files.

[KSSV]

There is no structure in the .mat file. Each file has just points and vel. So replace the line

v1 = out.vel ;

with

v1 = vel;

I have replaced the line in the answer.

[C.G.]

Thank you so much for your help.

[Stephen23]

Note that KSSV's answer loads directly into the workspace, which is not recommended.

You can make your code more robust by loading into an output variable (which is a scalar structure):

out = load(..);
out.vel