Load specific column from mat file

Hello, I got a mat file with a struct of different variables. Each variable got a 1X5 struct entry. MAT File:

a = [0 0 0 0 1]
b = [0 0 0 1 0]
c = [0 1 0 0 1]

My simulink model got different variants and each column of the matfile belongs to a variant. So I would like to load that mat file with only one column. Workspace:

a = 1
b = 0
c = 1

Is that possible? Greetings Lucas

Answer 1

[KSSV]

a = a(end) ;
b = b(end) ;
c = c(end) ;

Answer 2

[Jan]

This is not possible in one command, but with a tiny function:

function [a,b,c] = LoadColumn(FileName, col)
Data = load(FileName);
a = Data.a(col);
b = Data.b(col);
c = Data.c(col);
end

This might look trivial - in fact, it is. Does it solve your needs? If not, what is the remaining problem?

[Lucas Maiß]

I would like to extend that matfile also, therefore programming with the variable names isn't that useful.

I solved it now that way:

load('Mapping_Datein.mat'); 
mat.Field_Names = fieldnames(Dummy_Fzg);
mat.Cells = struct2cell(Dummy_Fzg); 
mat.Variante = 1; % Wahl der Variante
mat.Number_Variables = length(mat.Cells); 
mat.i = 1;

while(mat.i <= mat.Number_Variables)
    mat.string_spare = char(mat.Field_Names(mat.i));
    mat.Cell_spare = mat.Cells{mat.i,1};
    eval([['Fzg.' mat.string_spare] '=' num2str(mat.Cell_spare(mat.Variante))]);

      mat.i = mat.i + 1;
  end

clear ('mat', 'Dummy_Fzg');

But I thank you for your fast answer.

[Stephen23]

@Lucas Maiß: Your code is very inefficient, because of the conversion between numeric and string, and back again. You should really:

• load into a variable, as Jan Simon showed.
• Use dynamic field names instead of slow, inefficient and buggy eval:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Then you could easily avoid all of those pointless and slow conversions. Or as an alternative, here is a simpler solution using structfun:

>> a = [0 0 0 0 1];
>> b = [0 0 0 1 0];
>> c = [0 1 0 0 1];
>> save('test.mat','a','b','c')
>> S = load('test.mat');
>> T = structfun(@(v)v(end),S,'UniformOutput',0);
>> T.a
ans =  1
>> T.b
ans =  0
>> T.c
ans =  1

[Lucas Maiß]

That look good. Could you explain me what you are doing here: @(v)v(end)

[Jan]

@Lucas: @(v)v(end) is an anonymous function, which replies the last element of the input.

With a loop:

function S = LoadColumn(FileName, col)
S     = load(FileName);
Field = fieldnames(S);
for iField = 1:numel(Field)
   F     = Field{iField};
   S.(F) = S.(F)(end);
end
end