How to read specific lines from a text file and store them in a matrix?

Hello everyone,

I want to create a matrix from the attached text file that only includes the lines after the one that reads "#begindata". Basically, I want a matrix that includes the headers of the columns and all the numeric data from the file, but none of the information preceding it.

Also, would it be possible to use the same code when reading information from a file with a different number or rows and columns?

Thank you!

Answer 1

[Walter Roberson]

t = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/589822/20200926T000414.txt');
t(1:5,:)

ans = 5×7 table
       Var1           Var2        Var3    Var4    Var5    Var6    Var7
    __________    ____________    ____    ____    ____    ____    ____

    19/09/2020    00:00:00.231    -0.6    -0.6    0.4     12.1    15.2
    19/09/2020    00:00:10.220    -0.7    -0.6    0.4     12.1    15.2
    19/09/2020    00:00:20.223    -0.6    -0.6    0.4     12.1    15.2
    19/09/2020    00:00:30.230    -0.7    -0.6    0.4     12.1    15.2
    19/09/2020    00:00:40.232    -0.6    -0.6    0.4     12.1    15.2

[Remember Samu]

thank you so much it worked, now I need to create a column vector of Var4 column, how would I do that?

[Remember Samu]

Thank you, now i need to acess it as a matrix, how can i do that?

[Walter Roberson]

t{:,4}    %by number
t.Var4    %by name

[Remember Samu]

Thank you so much, the code seem to stop if there are any missing values, it will not access the whole column, it stops with an NaN. do you know how i can bypass this or if I can input 0 whenever it sees no value?

[Walter Roberson]

Could you give some example lines with missing values?

I scrolled through the data you posted but did not notice any missing entries.

[Remember Samu]

Thanks, please try access t(1:900,:) and see if it’s giving all the values. It is refusing

[Walter Roberson]

t = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/589822/20200926T000414.txt');
height(t)

ans = 60508

t(900:905,:)

ans = 6×7 table
       Var1           Var2        Var3    Var4    Var5    Var6    Var7
    __________    ____________    ____    ____    ____    ____    ____

    19/09/2020    02:29:50.228    1.9     -0.5    2.5     11.8     16 
    19/09/2020    02:30:00.214    1.9     -0.5    2.5     11.8     16 
    19/09/2020    02:30:10.217    1.8     -0.5    2.4     11.8     16 
    19/09/2020    02:30:20.221    1.8     -0.5    2.4     11.8     16 
    19/09/2020    02:30:30.223    1.8     -0.5    2.4     11.8     16 
    19/09/2020    02:30:40.213    1.8     -0.5    2.4     11.8     16 

I am not observing any problem. Which MATLAB release are you using?

[Remember Samu]

Hi I’m using R2019b, can you please do t(1:905,:)

[Walter Roberson]

There will be a delay while I install R2019b.

[Remember Samu]

Ok thank you so much.

[Walter Roberson]

I get a nan and NaT for the last entry (correspoding to the '#enddata' line), but otherwise it looks fine to me in R2019b on MacOS.

[Remember Samu]

Ok thank you so much, I will try it again,, thank you so much once again.

[Remember Samu]

Hi Walter, If I want to extract colums Var 1, Var 2 and Var 4 and put them into another variable named for expample refdata, how will I do it. Could you please help.

[Walter Roberson]

refdata = t(:,[1 2 4]);

Note that because Var1 and Var2 are not the same datatype as Var4, you cannot put the subset into a plain matrix, only composite datatype such as a table() or cell array.

Also, you might want to consider

t.dt = t{:,1} + t{:,2};
refdata = t(:, {'dt', 4});

[Remember Samu]

Hi Walter, Thank you so much.

[Remember Samu]

Hi Walter, I am facing the followign error:

Error using ValidationScriptupdated (line 11)

A table variable subscript must be a numeric array containing real

positive integers, a logical array, a character vector, a string

array, or a cell array of character vectors.

Line 10: t.dt = t{:,1} + t{:,2};

Line 11: refdata = t(:, {'dt', 4});

[Walter Roberson]

t.dt = t{:,1} + t{:,2};
refdata = [t(:, 'dt'), t(:,4)];

[Remember Samu]

Thank you so much Walter, It worked!