MATLAB: Dimension mismatch with growing char matrix

charfor loopmatrixsprintf

Hello,

I have in a loop Name_Pairs growing

Name_Pairs(1,:) = sprintf('%s%d','p',10)

then

Name_Pairs(2,:) = sprintf('%s%d','p',1)
Subscripted assignment dimension mismatch.

Name_Pairs is first a 1×3 char, then I try to put in a 1×2 char.

Any ideas on how could this be arranged? thank you

Best Answer

Example:

Name_Paris(1:10, 1:3) = ' ';   %initialize matrix to blanks
for k = 1 : 10
  s = sprintf('%s%d','p',k);
  Name_Pairs(1,1:length(s)) = s;
end

This would end up with ['p1 '; 'p2 '; 'p3 '; 'p4 '; 'p5 '; 'p6 '; 'p7 '; 'p8 '; 'p9 '; 'p10']

If you have R2016b or later you could instead do

Name_Pairs = strings(10, 1);
for k = 1 : 10
  Name_Pairs(k) = sprintf('%s%d','p',k);
end

Or more compactly,

Name_Pairs = string('p') + (1:10).' ;

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MATLAB: How to access a structure array using a loop

First, note that with your example, at the end p is a structure with just one field 'p10'. To create the structure you want:

p = struct('p1', {p1}, 'p2', {p2}, 'p3', {p3}, ...)

Also note that you don't need to put the field contents into a cell array, unless this content is itself a cell array. so:

 p = struct('p1', p1, 'p2', p2, ...)

may work just as well.

Secondly, your for loop is not going to work, ['p1' 'p2' 'p3' ...] is exactly the same as 'p1p2p3....', and i will take in turn the values 'p', then '1', then 'p' again, then '2', etc. You need to use a cell array

Finally, to use dynamic field names, you enclose the variable holding the field name in round brackets ().

So:

p = struct('p1',{p1}, 'p2',{p2}, 'p3',{p3}, 'p4',{p4}), 'p5',{p5}, 'p6',{p6}, 'p7',{p7}, 
'p8',{p8}, 'p9',{p9}, 'p10',{p10});
for fn = {'p1', 'p2', 'p3', 'p4', 'p5', 'p6', 'p7', 'p8', 'p9', 'p10'}
%or better: for fn = fieldnames(p)'
   o = p.(fn{1});
end

MATLAB: How to assign the value of a variable out of other variables

There are many ways to do this:

p_k = [p_g, p_a, num2str(p_n)]; %note the lack of quotes

Or my preference:

assert(mod(p_n, 1) == 0, 'p_n is not integer') %for the %d to work in sprintf, p_n must be integer
p_k = sprintf('%s%s%d', p_g, p_a, p_n);

And please, use more descriptive variable names.

Best Answer

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MATLAB: How to access a structure array using a loop

MATLAB: How to assign the value of a variable out of other variables

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