Replace a matrix on a text file

Hello everyone,

Few months ago I have done with the help of the forum a matlab code that extract a specific part of a 100 000+ rows text file as a matrix.

Using this matrix of 5 columns, I have created a "result" vector (called B) where values are numbers.

I would like to modify the part of the text file containing the initial matrix and replace it with my result vector which has the same number of rows but 1 column. Writematrix doesn't seem to work for specific location ?

So to be clear :

How can I replace an existing (n,5) matrix by a (n,1) at a specific location (that is known)?

Thanks for any help! If you like I can give you the file that is analysed to see how it works

Matt

Here is my code.

%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%A wannabe Code to read the t19 result file from Marc/Mentat and extract stress matrix  (part1) 
%Then, Calculate the Dang van criterion for critical element.
%                                                       Matthieu Aoun,
%                                                       01/22

clc
clear all

starter='=beg=52300 (Element Integration Point Values)                         '; %start of the matrix of interest
ender='=beg=52401 (Nodal Results)                                            '; %end of the matrix of interest

% Material Properties
% Material_name='Aluminium Al6061';
% E=640000;
sr0=94;      %tensile endurance limit released R=0
sr1=102;  %tensile Endurance limit fully reversed R=-1

alpha=(3/2)*(sr1-sr0)/(2*sr0-sr1);  % for tension/compression values
beta=(sr1*sr0)/(2*sr0-sr1); % for tension/compression values
% alpha = 0.232; % for bending/torsion
% beta = sr1*0.577; % for bending/torsion
xmax=beta/alpha;

try %if no error 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  matrix : Hydrostatic Stress, Von Mises, Sigma 1, Sigma 2, Sigma 3, Strain
%                                                          %    column      1                   2        3        4         5        6
%       CREATION OF RESULT MATRIX                          %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
file = 'G:\\Matthieu\\Job5\\topo1\\strut2\\file9\\marc9_job1.t19';
  
A  = textscan(fopen(file),'%s','delimiter', '\n'); %import file


stressloc1=find(strcmp(A{1,1},starter))+1   ;        %location of the beginning of the matrix
stressloc2=find(strcmp(A{1,1},ender))-2      ;               %location of the end of the matrix

range=stressloc2-stressloc1+1  ;                             %N of rows

opt = detectImportOptions(file, 'FileType','fixedwidth', 'VariableWidths',13*ones(1,6), 'ReadVariableNames',false);
opt.DataLines = [stressloc1,stressloc2];

%normal stresses and shear stress matrix 
nstress = readmatrix(file,opt);     nstress = nstress(:,1:5)  ;            
stresses(:,1)=abs((nstress(:,3)-nstress(:,5))*0.5); %tau13
stresses(:,2)=abs((nstress(:,4)-nstress(:,5))*0.5); %tau23
stresses(:,3)=abs((nstress(:,3)-nstress(:,4))*0.5); %tau12
stresses(:,4)=(nstress(:,3)+nstress(:,4)+nstress(:,5))/3; %sigmahydrosatic


%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                   DANG VAN CRITERION                     %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
maxnstress=max(stresses(:,4));
maxshear=max(stresses(:,1));

B=stresses(:,1)+alpha*stresses(:,4); 
safety=beta/max(B(:,1));

min_safety_el_id = find(B==max(B(:,1)))+10;
max_stress_el_id = find(stresses(:,4)==maxnstress)+10;

result_mat(count,1)=count; %USER RESULT
result_mat(count,2)=safety;
result_mat(count,3)=min_safety_el_id;
result_mat(count,4)=max_stress_el_id;
result_mat(count,5)=maxnstress;
result_mat(count,6)=maxshear;

catch %if error
    % skip this iteration
end
 
%%

Answer 1

[Voss]

You can do this using the low-level file I/O functions fopen(), fread(), fprintf(), and fclose().

An example of how to do it:

file = 'test.txt';
file_out = 'test_output.txt';

start_str = 'existence.';
end_str = 'More';

result = (10:10:60).';

fid = fopen(file);
file_data = fread(fid).';
fclose(fid);

s_idx = strfind(file_data,start_str);
e_idx = strfind(file_data,end_str);

result_data = reshape(sprintf('%g\n',result).',1,[]);

output_data = [ ...
    file_data(1:s_idx+numel(start_str)) ...
    result_data ...
    file_data(e_idx:end) ...
    ];

fid = fopen(file_out,'w');
fprintf(fid,'%s',output_data);
fclose(fid);

Showing the contents of the input and output files:

fid = fopen(file);
in_data = fread(fid);
fclose(fid);
fid = fopen(file_out);
out_data = fread(fid);
fclose(fid);
display(char(in_data.'));

Some stuff up
here I want to keep
because it is relevant
or important
or otherwise meaningful
to my existence.
Some stuff in here I want to replace
with something better, which I hope 
will serve me well in the future.
More stuff to keep down here.

display(char(out_data.'));

Some stuff up
here I want to keep
because it is relevant
or important
or otherwise meaningful
to my existence.
10
20
30
40
50
60
More stuff to keep down here.

[Matthieu Aoun]

Wow thanks a lot Benjamin, it is exactly what I needed, and way beter than my pseudo solution :

fid0=fopen(file,'r');

fid=fopen('test.t19','w');
BO = [A{:}];
% RES = [B{:}];
for j=1:stressloc1-1
tline=fgetl(fid0);
% fprintf(fid,'%s\n',char(BO(j,1)));
fprintf(fid,'%s\n',tline);
end

for i=1:size(B)
    fgetl(fid0);
fprintf(fid,'%13.6d%13.6d%13.6d%13.6d%13.6d\n',B(i,1),B(i,1),B(i,1),B(i,1),B(i,1));
% fprintf(fid,'%13.6E\n',B(i,1));
end

for k=stressloc2+1:size(A{1,1})
tline=fgetl(fid0);
% fprintf(fid,'%s\n',char(BO(j,1)));
fprintf(fid,'%s\n',tline);
% fprintf(fid,'%s\n',char(BO(k,1)));

end


fclose(fid)
fclose(fid0)

Considering I have 1 million+ lines, your solution is better.

Thanks again,

matt