Loop through list of variable in workspace to get and store in matrix

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joms
joms 2021-1-23
评论： joms 2021-1-25
How can i loop through list of variable 'selected' in workspace to get and store in one matrix (h).
it only stores the last matrix using my code. please help
clear
A=[1, 2, 3]'
B=[3,4,5]'
C=[3,7,9]'
x=who
selected={'A', 'B' 'C'};
m=length(selected)
h=zeros(3,m)
for cv = x
y= eval(sprintf('%1$s', cv{m}))
h(:,cv) = y
end
%%Result
A=[1 3 3;2 4 7; 3 5 9]
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joms
joms 2021-1-24
the data is from a matfile with saved signal, each has 1xn matrix. i just want to extract those data based on the signal list that i specify
selected={'A', 'B' 'C'};
and save it as new matrix to print as csv.i used this method because there are some signals in the list not available in the matfile and want to substitute by zeros. Do you have more efficient method of extracting specifice struct data from workspace? thank you.
Stephen23
Stephen23 2021-1-24
编辑：Stephen23 2021-1-24
"Do you have more efficient method of extracting specifice struct data from workspace? thank you."
NO, there is no efficient way to do this: once the data is in the workspace as lots of separate variables, you have forced yourself into writing slow, complex, inefficient, obfuscated code to try and access it. The best approach is to avoid needing to do this, which is easy to do.
"the data is from a matfile with saved signal, each has 1xn matrix."
Then you can easily write neat, simple, efficient code by loading into one variable when you load the data into the workspace, exactly as the MATLAB documentation shows:
https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html
It is much better to avoid the bad situation that you are getting yourself into, by simply writing simple robust code, e.g. by loading into an output variable:
S = load(..)
And storing that data in one variable, exactly as the documentation shows.

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Walter Roberson
Walter Roberson 2021-1-24
selected={'A', 'B' 'C'};
filename = 'YourFile.mat';
vars_present = who('-file', filename);
present_mask = ismember(selected, vars_present);
present_idx = find(present_mask);
num_selected = length(selected);
datacell = cell(1, num_selected);
for cv = present_idx
varname = selected{cv};
datastruct = load(filename, varname);
datacell{cv} = datastruct.(varname);
end
if isempty(present_idx)
%NONE of the vars are present. Use 0 all around
datacell(1:num_selected) = {0};
else
%fill in the missing the same size as the first that exists
numrow = size(datacell(present_idx{1}), 1);
datacell(~present_mask) = {zeros(numrow,1)};
end
h = cell2mat(datacell);
%now write out h to appropriate csv file
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