[R2017a] save nested structure with save, append files, load it and check some 'string' fields with strcmp

Hey guys,

I am working on a GUI that allows users to save the data, initially in a text file, inside a nested structure into a file .m

clc; clear;
s1(1).name = 'CaCO3.....';
s1(1).time = [0 1 2 3 4 5 6 7 8 9 10];
s1(1).mass = [0.9,0.9,0.8,0.7,0.7,0.5,0.4,0.4,0.4,0.,4];
s1(1).heat = [0 1 2 3 4 5 6 7 8 9 10];
s1(2).name = 'MgCO3.....';
s1(2).time = [0 2 4 6 8 10 12 14 16 18];
s1(2).mass = [1 1 1 1 1 1 1 1 1 1];
s1(2).heat = [9 9 9 9 9 9 9 9 9 9];
save('newstruct.mat', 's1');
disp('Contents of newstruct.mat:')
whos('-file', 'newstruct.mat')
clear('s1')
load('newstruct.mat')
A_cell = struct2cell(s1);

I want now to access all the field s1.name and check if among those there is a particular string, let's say 'CaCO3.....'.

Both:

[s1.name]
[A_cell{1,1,:}]

give me the following result: 'CaCO3.....MgCO3.....'

my questions are:

1) How can I put all results in an array? Or if I want to loop, how can I know the total length of the field .name?

2) If the name doesn't exist, how do I create a new substrcture s1(3)?

Answer 1

[Walter Roberson]

lookfor = 'CaCO3';
names = {s1.name};
[~, idx] = ismember(lookfor, names);

if idx == 0
  idx = length(s1)+1;
  s1(idx).name = lookfor;
end

s1(idx).time = new time information
s1(idx).mass = new mass information
s1(idx).heat = new heat information

[Michael Daldini]

What to say... thank you!

Let's imagine that now the structure is composed by s1(1), s1(2), s1(3); how can I delete s1(2)? Will s1(3) become the new s1(2)? If not, will empty s1(2) be detected as nested structure and be shown in a listbox (guide)?

How did you learn these things? Could you suggest me a good tutorial, book, video to follow? Thank you again

[Stephen23]

"how can I delete s1(2)? "

Just like with any other array:

   s1(2) = []

"Will s1(3) become the new s1(2)?"

Yes, just like with any other type of array. You can try it yourself:

>> V = 1:3
V =
   1   2   3
>> V(2) = []
V =
   1   3

"How did you learn these things?"

By reading the documentation a lot, and by reading lots of answers on this forum. Also by experimenting: you could have easily tried it yourself, with a small 1x3 structure, and seen what happens.

"Could you suggest me a good tutorial, book, video to follow?"

Very few of the third-party books or online tutorials I have seen have been very good: some of them are quite dated, or teach inefficient practices, or give outright bad advice. The best source of information about learning MATLAB is... the MATLAB documentation:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

https://www.mathworks.com/help/pdf_doc/matlab/index.html

You might like to read this:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

[Michael Daldini]

Thank you again :) I could have tried but I was on the phone and i wanted to be sure to have a solution to the time I would get to the notebook :)

Thank you again, I will start reading a lot.