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

Question

joms 2021-1-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/724987-loop-through-list-of-variable-in-workspace-to-get-and-store-in-matrix

评论： joms 2021-1-25

采纳的回答： Walter Roberson

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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 2021-1-24

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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 2021-1-24

编辑：Stephen23 2021-1-24

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"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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Answer 1

Walter Roberson 2021-1-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/724987-loop-through-list-of-variable-in-workspace-to-get-and-store-in-matrix#answer_604927

在 MATLAB Online 中打开

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