How to extract specific data from a txt file

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!

Answer 1

[Star Strider]

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.

.

Answer 2

[Mayur]

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);

You can read more about textscan here: https://www.mathworks.com/help/matlab/ref/textscan.html