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Sandwiching "num2str" in between file-naming loop.

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I'm trying to create an automated loop to extract data from .txt files that are generated from a different script. <NoNodes> is describing for a variable such that NoNodes = [16, 36, 64, 100, 144 . . . (n-2)^2, n^2]. Just squaring even integers starting at 4.
The real issue I am having is solving for <myfilename(i)>. I've put a code break at line that defines <Stress> so I can see the affects. It combines strings in a way that I do not understand and generates numbers I do not know how they've been solved.
I.e. for i = 1, this is the string output I got:
ans =
"CombinedStresses.Periodic.N49CombinedStresses.Periodic.N54"
Any idea's for the code below?
N = 100;
NoNodes = (4:2:N).^2
A = "CombinedStresses.Periodic.N%u";
B = ".Z5.Gaussian.Data.10_08_2020.Trial.1.txt";
for i = 1:length(NoNodes);
myfilename(i) = sprintf(A, num2str(NoNodes(i)), B);
filename = fullfile('D:\University\Fall 2020\Class\HW3\Raw Data\Stresses', myfilename);
Stress = readtable(myfilename(i));
end
  1 Comment
Walter Roberson
Walter Roberson on 9 Oct 2020
no it doesn't. The num2str gives '16' which is char(49 54) and the %u converts the char(49) to '49'. The vector is not finished outputting so it repeats the format and converts the char(54) to '54'. So you end up with like 'PQR49PQR54'

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Accepted Answer

Walter Roberson
Walter Roberson on 9 Oct 2020
N = 100;
NoNodes = (4:2:N).^2
A = "CombinedStresses.Periodic.N";
B = ".Z5.Gaussian.Data.10_08_2020.Trial.1.txt";
for i = 1:length(NoNodes);
myfilename(i) = A + NoNodes(i) + B;
filename = fullfile('D:\University\Fall 2020\Class\HW3\Raw Data\Stresses', myfilename(i));
Stress = readtable(filename);
end
The problem you had was you have a %u format element in your format, which was the content of A, but you were passing in the corresponding position the content of num2str(16) . The result of num2str(16) is '16' which is char([49 54]) . The character codes were converted through the %u format item.
  2 Comments
Walter Roberson
Walter Roberson on 9 Oct 2020
A quite valid alternative for you would have been
N = 100;
NoNodes = (4:2:N).^2
A = "CombinedStresses.Periodic.N";
B = ".Z5.Gaussian.Data.10_08_2020.Trial.1.txt";
for i = 1:length(NoNodes);
myfilename{i} = sprintf('%s%u%s', A, NoNodes(i), B);
filename = fullfile('D:\University\Fall 2020\Class\HW3\Raw Data\Stresses', myfilename{i});
Stress = readtable(filename);
end
When you use " around a list of characters, you are defining a string() object, which is distinct from a character vector. string() objects have methods defined for them that are not available for character vectors.
When you have a character vectors P and Q, the P+Q operation is defined like double(P)+double(Q) -- and has the same limitations such as one of them having to be scalar or else the two having to be the same length.
>> 'ABC'+1, char(ans)
ans =
66 67 68
ans =
'BCD'
However, for string() objects P and Q, the P+Q operation is defined to be string concatenation, like
string(strcat(cellstr(P), cellstr(Q)))
and furthermore, if one of P or Q is string and the other is numeric, then the P+Q operation is like
string(strcat(cellstr(string(P)), cellstr(string(Q))))
and string() applied to a numeric value is something like num2str() of the numeric value.
"F" + (1:5)
would construct ["F1" "F2" "F3" "F4" "F5"] which is a string array of size 1 x 5, and indexing at (1) would be "F1" .
There is no float() operation because the operating involved is concatenation not arithmetic.

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