How to post process each variable in a mat file ?

I am trying to downsample all the variables in a mat file.

I can use downsample(var, newSampling) to downsample an individual variables but what to do if i need to downsample all the vectors in the mat file.

load ('my_mat_file_here.mat')

list_var = who; % to get the list of variables

for kk = 1:1:length(list_var) % to run the loop

% downsample(eval(list_var{kk}),10); <-- this part is working as expected with eval

[list_var{kk} '_1hz'] = downsample(eval(list_var{kk}),10);

end

% in this part how to define a new variable

% i am trying to use the variable name from list_var which is a character

% and add _1hs to ths string but matlab won't allow it to % be used as a varaible name

% trying to avoid using assignin & eval to assign the new variable to my base workspce

% any help appreciated.

Answer 1

[Walter Roberson]

S = load(filename)
fn = fieldnames(S)
Fc = length(fn)
for k = 1 : Fc
  F = fn{k}
  Data = S.(F)
  Process Data
end

[Shekhar Vats]

It worked for me.

Thank you Walter for a quick and helpful response. Do not know why i was shying away from using structure and accesing variables inside it.

Answer 2

[Shekhar Vats]

% Downsampling a given 'X' hz file to a input 'Y'hz file

%This script will load the file in a structure and append _YHz

% at the end of current variables. It will save the new file with the old

% name and append _down_sampled to it

% NOTE --> It will only DOWNSAMPLE the file. Although it can do up

% sampling, but it's not recommended to up sample data as it will just

% interpolate the data in between two points.

% You will need matlab SIGNAL PROCESSING TOOLBOX for this script to work

% In case you do not have access to the toolbox, please contact the author

% remote desktop matlab151a and matlab 151b have Signal Processing Toolbox

%% prompt dialog

tic;

prompt = {'Enter current data frequency[hz]:','Enter desired data frequency[hz]:'};

dlgtitle = 'Downsample data'; % dialog title

dims = [1 40];

definput = {'10','1'};

answer = inputdlg(prompt,dlgtitle,dims,definput);

%% post processing of dialoge

current_freq = str2double(cell2mat((answer(1,1))));

desired_freq = str2double(cell2mat(answer(2,1)));

dwn_smpl = current_freq/desired_freq; % desired downsampling frequency

str_var = ['_' num2str(desired_freq) 'Hz']; % var name append

%% file info

[f_name, f_path]= uigetfile({'*.mat'}, 'Select a mat file'); % select the file(s) from gui

File = [f_path '\' f_name]; % getting the file path and name

S = load(File); % loading file to a structure

fn = fieldnames(S); % get the variable names in the file.

Fc = length(fn); % num of variables in the structure file

for k = 1:1:Fc; % running look to process data

F = fn{k}; % field variable name

F = strrep(F, 'YOUR TEXT GOES HERE', ''); % replacing undesireable text from variable name

if dwn_smpl > 1

S.([fn{k} str_var]) = downsample(S.(F),dwn_smpl); % downsampling data

else

S.([fn{k} str_var]) = upsample(S.(F),dwn_smpl); % up sampling data

end

end

%% saving file based off up sampling or down sampling

if dwn_smpl > 1

save([f_name(1:end-4) '_down_sampled.mat'], '-struct', 'S') % extracting data from structure and saving as .mat file

else

save([f_name(1:end-4) '_up_sampled.mat'], '-struct', 'S') % extracting data from structure and saving as .mat file

end

disp (['All variables down sampled to: ' num2str(desired_freq) 'Hz']);

toc