extract numbers from specific lines in text file

Question

Petr Michalek 2022-11-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1865438-extract-numbers-from-specific-lines-in-text-file

评论： Askic V 2022-11-29

采纳的回答： Askic V

在 MATLAB Online 中打开

Hello,

I have a .txt file with mixed measurement data and text. There are lines with coordinates which look like like this:

(mm,mm,mm,deg): 45 250 0 0

I want to extract the numbers only. The lines are located regularly in the file at line numbers 207, 60232, 120257, etc., i.e. after every 60025 lines.

I have written the code, that reads the specific lines: (points is number of measured points and name is name of measurement file)

last_coord=(points-1)*60025+207; 
coord_line=207:60025:last_coord;
coords=cell(1,points); range_coords=cell(1,points);
for i=1:points
 range_coords{i}=[coord_line(i) 2 coord_line(i) 5];
 coords{i}=readmatrix(name, 'Range', range_coords{i});    
end

However, this code works only for first two readings of coordinates at lines 207 and 60232, for the third reading and onward I get [NaN,NaN,NaN,NaN].

I checked the file up to the sixth coordinates, the lines look the same as the example here and are located on the correct line number. Please help.

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Jiri Hajek 2022-11-28

Hi, this behaviour could have several causes, so I'd suggest to try and debug the problem in a slightly greater detail. E.g. try to set the output typa as text by adding name-value argument to your readmatrix command. This way, you will be able to analyze the data supplied by the command...

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Answer 1

Askic V 2022-11-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1865438-extract-numbers-from-specific-lines-in-text-file#answer_1114033

在 MATLAB Online 中打开

coord.txt

Would something like this satisfy your need?

fid = fopen('coord.txt');
tline = fgetl(fid);
search_str = '(mm,mm,mm,deg):';
matrix = [];
while ischar(tline)
    k = strfind(tline, search_str);
    if ~isempty(k)
       matrix = [matrix; str2num(tline(k + length(search_str) : end))] 
    end
    % read next line
    tline = fgetl(fid);
end
% close the file
fclose(fid);

I have used the attached txt file to test this code snippet.

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Petr Michalek 2022-11-29

Your code works fine, thanks.

Askic V 2022-11-29

Yes, but keep in mind it is not efficient, because matrix changes size on each iteration. Much better solution is to preallocate matrix at the begining. But if you don't have a lot of data, this solution could be fine also.

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