how to change multiple items in a text file?

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Idin Pushkin 2019-5-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459990-how-to-change-multiple-items-in-a-text-file

评论： Stephen23 2019-5-10

采纳的回答： Stephen23

bp.txt

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hello

i have a text file with name of bp. u see many 'TSTEP' in this file. there are other written text just below them like: '1*100'. now i want to find these 'TSTEP's and make changes on the text below them (just changing the number before the asterisk). for example '1*100' is going to be '2.5*100' or any other number can be replaced. i use this code when i have one 'TSTEP' in file. ut it doesnt work for the cases when there are more than one of it. the number of TSTEPs may differ from file to file. is it possible to do that?

thanks in advance

clc;
fid=fopen('bp.txt','r');
c=textscan(fid,'%s','delimiter','\n','Whitespace','','CommentStyle','1','CollectOutput',0);
fclose(fid);
c=string(c{:})
iz=find(contains(c,"TSTEP"));
d1=['2.5','*',extractAfter(c{iz+1},'*')];
d2=replace(c,c{iz+1},d1);
fid = fopen('bp.txt','w');
for j= 1:length(d2)
    fprintf(fid, '%s\n', char(d2{j}));
end
fclose(fid);

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采纳的回答

Stephen23 2019-5-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459990-how-to-change-multiple-items-in-a-text-file#answer_373446

编辑：Stephen23 2019-5-7

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EDIT: much faster:

rpl = '2.5'; % the new value (you can generate this using NUM2STR).
str = fileread('bp.txt');
str = strtrim(regexp(str,'\n','split'));
idx = 1+find(strcmpi(str,'TSTEP'));
str(idx) = regexprep(str(idx),'^[^*]+',rpl);
fid = fopen('pb_new.txt','wt');
fprintf(fid,'%s\n',str{:});
fclose(fid);

ORIGINAL (SLOW): With a simple regular expression and regexprep:

rpl = '2.5'; % the new value (you can generate this using NUM2STR).
rgx = '(?<=\s+TSTEP\s+)\d+(?=\*100)'; % regular expression.
% Read old file and replace data:
old = fileread('bp.txt');
new = regexprep(old,rgx,rpl);
% Save the new file:
fid = fopen('bp_new.txt','wb');
fprintf(fid,'%s',new);
fclose(fid)

The input and output files are attached.

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Stephen23 2019-5-6

编辑：Stephen23 2019-5-7

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"when the above code in run, no error is given but, it does not replace the number before '*' with new number."

I would not expect MATLAB to change anything in "c.txt", because that is not the filename that you have used in your code. Your example file is named "c.txt", and your code is reading and writing to "bp.txt".

When I changed your code to read "c.txt" and write "d.txt" it worked perfectly (the input file "c.txt", the output "d.txt", and code file "bp0.m" are all attached). So far the code works exactly as expected, and has changed the file values correctly every time that I have run it.

"the other point is it is too slow. is there anyway to make it more fast?"

Of course! The advantage of my original answer is that the file does not change any other characters (e.g. same newline characters). But you can considerably speed up the code if that is not a requirement. You will find that this is a lot faster:

rpl = '6'; % the new value (you can generate this using NUM2STR).
str = fileread('c.txt');
str = strtrim(regexp(str,'\n','split'));
idx = 1+find(strcmpi(str,'TSTEP'));
str(idx) = regexprep(str(idx),'^[^*]+',rpl);
fid = fopen('e.txt','wt');
fprintf(fid,'%s\n',str{:});
fclose(fid);

Once again I tested this to make sure that it works (the input file "c.txt", the output "e.txt", and code file "bp1.m" are all attached)

Idin Pushkin 2019-5-6

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bb.txt

is there any way to write the original file on itself with this code? this code works perfectly but the output file name is different from the original one and i want to be the same.

in this code:

rpl = '6'; % the new value (you can generate this using NUM2STR).
str = fileread('c.txt');
str = strtrim(regexp(str,'\n','split'));
idx = 1+find(strcmpi(str,'TSTEP'));
str(idx) = regexprep(str(idx),'^[^*]',rpl);
fid = fopen('e.txt','wt');
fprintf(fid,'%s\n',str{:});
fclose(fid);

i want to overwrite the output file on the original file so i changed 'e.txt' to 'c.txt', every time i run the code with different 'rp1', and it is seen that:

'80*100 /' 'rp1=7' it becomes '70*100'

'70*100 /' 'rp1=12' it becomes '120*100'

what i want to say is it overwrites some part of new number on old number when input and output files have the same name. but for cases with different names of input and output file name it works correctly.

i want the output file has the same name as the input file.

Idin Pushkin 2019-5-9

编辑：Idin Pushkin 2019-5-9

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str = fileread('bp.txt');
%                       ^^^^ What is this supposed to do?

it was spelling mistake about the above code. about the loop u said i use this code and doesnt work again

for i=1:length(vec)
    str(idx) = regexprep(str(idx),'^[^*]+',num2str(vec(i)));
    fid = fopen(newStr1,'wb');
    fprintf(fid,'%s\n',str{:});
    fclose(fid);
end

Stephen23 2019-5-10

I wrote "with indexing into the vectors idx and vec..."

You are using i with vec (which is good) and ignored idx (which is not good).

You can see that the elements of idx correspond to the elements of vec... therefore if you use indexing into vec then you will also need exactly the same indexing into idx (just as I wrote in my comment).

Note the putting the file writing code inside that loop just overwrites the file contents on each iteration. In the end, only the last iteration will remain, so there is no point in this being isnide the loop (apart from slowing down your code and heating up your room).

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