How to extract specific data from a txt file

Question

Sydney McLachlan 2023-6-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1987319-how-to-extract-specific-data-from-a-txt-file

回答： Mayur 2023-6-23

Niskin-Logger-Sample.txt

Hi there!

I have a txt file that contains lines starting in either U4 or U6. I want to filter out all the lines with U4 so I'm left with only the ones that contain U6. How would I go about that?

Thanks in advance!

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Answer 1

Star Strider 2023-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/1987319-how-to-extract-specific-data-from-a-txt-file#answer_1261408

在 MATLAB Online 中打开

Niskin-Logger-Sample.txt

Using my code from my earlier Comment, one approach would be—

% type('Niskin-Logger-Sample.txt')

opts = detectImportOptions('Niskin-Logger-Sample.txt', 'Delimiter',{' '});

opts = setvaropts(opts, 'Var3', 'InputFormat','MM/dd/uuuu'); % Guessing The Date Format

T1 = readtable('Niskin-Logger-Sample.txt', 'Delimiter',{' '});

Warning: The DATETIME data was created using format 'MM/dd/uuuu' but also matched 'dd/MM/uuuu'.
To avoid ambiguity, supply a datetime format using SETVAROPTS, e.g.
opts = setvaropts(opts,varname,'InputFormat','MM/dd/uuuu');

T2 = readtable('Niskin-Logger-Sample.txt', 'HeaderLines',50)

T2 = 8826×4 table

Var1 Var2 Var3 Var4 ______ ______ ____ __________ {'U4'} 5.5718 298 {0×0 char} {'U4'} 5.9434 298 {0×0 char} {'U4'} 4.8241 298 {0×0 char} {'U4'} 4.967 298 {0×0 char} {'U4'} 5.0333 298 {0×0 char} {'U4'} 4.7708 298 {0×0 char} {'U4'} 5.1185 298 {0×0 char} {'U4'} 4.837 298 {0×0 char} {'U4'} 4.9518 298 {0×0 char} {'U4'} 5.0625 298 {0×0 char} {'U4'} 4.7761 298 {0×0 char} {'U4'} 5.1258 298 {0×0 char} {'U4'} 4.8705 298 {0×0 char} {'U4'} 4.9459 298 {0×0 char} {'U4'} 5.0957 298 {0×0 char} {'U4'} 4.7892 298 {0×0 char}

[UVar1,~,ix] = unique(T2.Var1);

Um = accumarray(ix, (1:numel(ix)).', [], @(x){T2(x,:)})

Um = 2×1 cell array

{8574×4 table} { 252×4 table}

U6 = Um{2}

U6 = 252×4 table

Var1 Var2 Var3 Var4 ______ ____ __________ __________ {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char} {'U6'} NaN 1.6868e+09 {0×0 char}

U6Var2NotNaN = U6(~isnan(U6.Var2),:)

U6Var2NotNaN = 0×4 empty table

NrVar2NaN = nnz(isnan(U6.Var2))

NrVar2NaN = 252

So ‘Var2’ (whatever it is) has only NaN values for the entire ‘U6’ table.

.

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Answer 2

Mayur 2023-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/1987319-how-to-extract-specific-data-from-a-txt-file#answer_1261428

在 MATLAB Online 中打开

Hi Sydney!

I understand that you want to extract specific lines from a .txt file, here particularly lines starting with 'U6'. You can use the following code snippet:

fid = fopen('Niskin-Logger-Sample.txt', 'r');
data = textscan(fid, '%s', 'Delimiter', '\n');
fclose(fid);
u6_lines = data{1}(startsWith(data{1}, 'U6'));
disp(u6_lines);