How to skip lines of Data in a middle of a text file

I am trying to analyze a textfile and skip the three lines in the textfile that begin with the character I, V, or D and only read the lines that begin with R. The I,V,D lines are random throughout the document but always appear sequentially. Basically, i want the code to restart after finishing with the last line of data that begins with an R and restart once it sees the next data line that begins with an I. This is my code so far, that will skip the first I,V,D lines that it sees and read and manipulate the R lines but then it stops. Also attached in example of the data

syms X Y z
fid = fopen('extractcdb.txt','r');
count =0;
chr= ('I''V''D''R');
tf= ischar(chr);
for chr = ('I''V''D') 
    tline = fgets(fid);
    continue
end
    for chr= ('R')        
        tline = fgets(fid);
        A = textscan(fid, '%*s %*s %*s %*f %*f %*d %*f %*d %*d %d %*d','Delimiter',',');
        Ad = cell2mat(A);
        B = [diff(Ad)]*1.2;
        B =[zeros(length(Ad) - length(B),1);B];
        for   i = 1
              z = 1:708
              C = cumsum(B(i+z)) + Ad(i)
        end 
    end

Answer 1

[Star Strider]

Try this:

fidi = fopen('extractcdb.txt','rt');
k1 = 1;
while ~feof(fidi)
    for k2 = 1:3
        StepInfo{k1,k2} = fgetl(fidi)                   % ‘Step Information’ Section Header Lines Cell Array
    end
    C = textscan(fidi, ['R' repmat('%f',1,10)], 'Delimiter',',', 'CollectOutput',true);
    M = cell2mat(C);
    if isempty(M)                                       % Empty Matrix Indicates End-Of-File In Case Of Missing ‘End-Of-File’ Indicator
        break
    end
    D{k1,:} = M;                                        % Section Matrices
    fseek(fidi, 0, 0);
    k1 = k1 + 1;
end
fclose(fidi);
Out = cell2mat(D);                                      % Optional, You May Want To Keep The Segments Separate

This produces ‘D’ as:

D =

  4×1 cell array

    {712×10 double}
    {712×10 double}
    {866×10 double}
    {854×10 double}

and ‘StepInfo’ as a (5x3) cell array of the section header lines in the event that you need that information.

[Bradley Sprinkle]

Thank you but your code is not quite working for my data file. it gives me a 'Expected one output from a curly brace or dot indexing expression, but there were 0 results.' error

[Star Strider]

It ran for me without error with the file you posted in R2019a.

What line threw the error?

Did you make any changes to my code?

[Bradley Sprinkle]

I'm sorry perhaps it is because I forgot to mention i am running 2018b?

[Star Strider]

I just ran it as posted in R2018b (Update 4) and it again ran without error.

What line is throwing the error?

Did you make any changes to my code?

[Bradley Sprinkle]

No changes were made.

D{k1,:} = M; is causing the error

[Star Strider]

That doesn’t make sense.

Just after the ‘M’ assignment put whos('M'):

    M = cell2mat(C);
    whos('M')

the result should be:

  Name        Size            Bytes  Class     Attributes
  M         712x10            56960  double  

for the first one, similar results for the others, and:

  Name      Size            Bytes  Class     Attributes
  M         0x10                0  double

for the last one.

Please post the results you get.

[Bradley Sprinkle]

StepInfo =

  1×3 cell array

    {'I,NGB,unknown,|,|,…'}    {'V,|,P,446000682846…'}    {'D,|,|'}


StepInfo =

  1×3 cell array

    {'I,NGB,unknown,|,|,…'}    {'V,|,P,446000682846…'}    {'D,|,|'}


StepInfo =

  1×3 cell array

    {'I,NGB,unknown,|,|,…'}    {'V,|,P,446000682846…'}    {'D,|,|'}

  Name        Size            Bytes  Class     Attributes

  M         712x10            56960  double              

Expected one output from a curly brace or dot indexing expression, but there were 0
results.

Error in Untitled15 (line 13)
    D{k1,:} = M; 

This is the output after running the code

[Star Strider]

Something is interfering with my code as your are using it.

Using it as a function may solve that, since functions have their own workspaces.

Save this as ImportSpecialTextFile.m on your MATLAB user search path:

    function [D,StepInfo] = ImportSpecialTextFile(filename)
        fidi = fopen(filename,'rt');
        k1 = 1;
        while ~feof(fidi)
            for k2 = 1:3
                StepInfo{k1,k2} = fgetl(fidi);                  % ‘Step Information’ Section Header Lines Cell Array
            end
            C = textscan(fidi, ['R' repmat('%f',1,10)], 'Delimiter',',', 'CollectOutput',true);
            M = cell2mat(C);
            if isempty(M)                                       % Empty Matrix Indicates End-Of-File In Case Of Missing ‘End-Of-File’ Indicator
                break
            end
            D{k1,:} = M;                                        % Section Matrices
            fseek(fidi, 0, 0);
            k1 = k1 + 1;
        end
        fclose(fidi);
    end

Then call it as:

filename = 'extractcdb.txt';
[D,StepInfo] = ImportSpecialTextFile(filename)

EDIT — Added ‘save to .m file’ note. Code unchanged.

[Bradley Sprinkle]

it is giving me this error:

 function [D,StepInfo] = ImportSpecialTextFile(filename)
 ↑
Error: Function definition not supported in this context. Create functions in code
file.

[Star Strider]

Save it as:

ImportSpecialTextFile.m 

on your MATLAB user search path.

[Bradley Sprinkle]

I apologize for all the issues (I don't have much experience coding with Matlab but am required to learn). But when i save the file it gives me the same error and if i look specifically at line 2 (the line giving an error), it says 'Unable to define local function 'ImportSpecialTextFile' because it has the same name as the file'. I checked that path and it is indeed being saved to the user search path.

[Star Strider]

My code works correctly for me and runs without error in R2018b (Update 4) and R2019a (Update 3).

In your script file (not the function file), call my function as:

filename = 'extractcdb.txt';
[D,StepInfo] = ImportSpecialTextFile(filename)

It should return the ‘D’ and ‘StepInfo’ variables to your workspace. It does when I run it, and returns:

D =

  4×1 cell array

    {712×10 double}
    {712×10 double}
    {866×10 double}
    {854×10 double}


StepInfo =

  5×3 cell array

    {'I,NGB,unknown,|,|,|,|…'}    {'V,|,P,446000682846,60…'}    {'D,|,|'       }
    {'I,NGB,unknown,|      …'}    {'V,|  ,P      ,4460006…'}    {'D,|  ,|'     }
    {'I,NGB,unknown,|      …'}    {'V,|  ,N      ,4460006…'}    {'D,|  ,|'     }
    {'I,NGB,unknown,|      …'}    {'V,|  ,N      ,4460006…'}    {'D,|  ,|'     }
    {[           -1.0000e+000]}    {[           -1.0000e+000]}    {[-1.0000e+000]}  

You would call the ‘D’ matris (for example to use the first cell) as:

    D1 = D{1}

the first five lines of it being:

D1 =

  Columns 1 through 7

            1            0       0.7079      0.63298          420       32.251        32768
            2            0      0.69802      0.62581         1080       32.439            0
            3            0      0.68223      0.61658         1620       32.945        32768
            4            0      0.66922      0.61025         2280         33.4            0
            5            0      0.65896      0.60567         2880       33.778            0

  Columns 8 through 10

        18557        16593        42272
        18298        16405        42518
        17884        16163        43181
        17543        15997        43778
        17274        15877        44273

I have no idea if the lack of updates could be a problem in your not being able to run my code, however if you have not updated your R2018b installation, follow the steps I outlined in 2018b Update 3 (link) to update it. Note that there are four updates.

[Bradley Sprinkle]

I updated my matlab and it works. Thank you very much

[Star Strider]

As always, my pleasure!