MATLAB: Importing specific rows of Data from Text file

import from text fileMATLABspecific row import from text file

Hi;
I am having some sensor data which is a very large text (.dat) file. Some of the relevant data from this file needs to be analyzed and plotted through help of MATLAB.
The example for the data is like:
C 0 0.001 -0.02 24.09 4.64 -100.00 -100.00
C 0 1.005 0.29 24.09 4.43 -100.00 -100.00
C 0 2.009 -0.34 24.09 8.26 -100.00 -100.00
C 0 3.014 -0.18 24.06 6.06 -100.00 -100.00
C 0 4.018 0.07 24.06 5.61 -100.00 -100.00
C 0 5.022 0.02 24.09 4.92 -100.00 -100.00
C 0 6.026 0.34 24.12 4.28 -100.00 -100.00
C 0 7.030 -0.46 24.09 8.37 -100.00 -100.00
C 0 8.034 -0.23 24.09 7.50 -100.00 -100.00
R 0 60.275 -0.157674 -0.006891 0.000000 ……
Now all I want to import to MATLAB and analyze is the rows which start with this alphabet 'R' , which stands for Result. There is a pattern to the occurrence of 'Result' data in this big text file. The 'R' row occurs at an interval of every 160 rows.
How can I achieve this solution to import only these rows which tell the 'Result' into MATLAB, maybe interactively or programmatically. I would deeply appreciate a detailed answer as I am on intermediate level of MATLAB programming.
Thank you so much in advance! Pramit

Best Answer

If the entire file fits in memory, try this code
    >> num = cssm()
    num =
             0   60.2750   -0.1577   -0.0069         0
             0   60.2750   -0.1577   -0.0069         0
             0   60.2750   -0.1577   -0.0069         0
             0   60.2750   -0.1577   -0.0069         0
where
    function    out = cssm()
        %   read the entire file to one cell array with one row per cell
        fid = fopen( 'cssm.txt', 'r' );
        cac = textscan( fid, '%s', 'Delimiter', '\n' );
        [~] = fclose( fid );
        %   find rows which begin with 'R'.  
        isR = cellfun( @(str) strncmp(strtrim(str),'R',1), cac{:} );
        %   extract the rows beginning with 'R' 
        rlt = cac{:}(isR);
        %   join all rows with results to one long string separated by '\n'
        one_str = strjoin( rlt, '\n' );
        %   parse the string. 

        result  = textscan( one_str, '%c%f%f%f%f%f', 'CollectOutput',true ); 
        %   make sure that only results are included in the output

        assert( strcmp( unique(result{1}), 'R' )     ...
            ,   'Non-result rows included in result' )
        out = result{2};
    end
and where cssm.txt contains
    C 0 6.026 0.34 24.12 4.28 -100.00 -100.00
    C 0 7.030 -0.46 24.09 8.37 -100.00 -100.00
    C 0 8.034 -0.23 24.09 7.50 -100.00 -100.00
    R 0 60.275 -0.157674 -0.006891 0.000000
    C 0 6.026 0.34 24.12 4.28 -100.00 -100.00
    C 0 7.030 -0.46 24.09 8.37 -100.00 -100.00
    C 0 8.034 -0.23 24.09 7.50 -100.00 -100.00
    R 0 60.275 -0.157674 -0.006891 0.000000
    C 0 6.026 0.34 24.12 4.28 -100.00 -100.00
    C 0 7.030 -0.46 24.09 8.37 -100.00 -100.00
    C 0 8.034 -0.23 24.09 7.50 -100.00 -100.00
    R 0 60.275 -0.157674 -0.006891 0.000000
    C 0 6.026 0.34 24.12 4.28 -100.00 -100.00
    C 0 7.030 -0.46 24.09 8.37 -100.00 -100.00
    C 0 8.034 -0.23 24.09 7.50 -100.00 -100.00
    R 0 60.275 -0.157674 -0.006891 0.000000
&nbsp
... and an alternative, which is an order of magnitude faster
    function    out = faster()
        %   read the entire file to one string
        str = fileread( 'cssm.txt' );
        %   find start and end indicies of all the "rows" beginning with 'R'
        xpr = '(?<=\s)R[^(\n|\r)]+(\n|\r){1,2}';
        [ix1,ix2] = regexp( str, xpr, 'start', 'end' );
        %   extract the "rows" beginning with 'R'
        isi = false(1,length(str)); 
        for ii = 1:length(ix1)
            isi(ix1(ii):ix2(ii))=true; 
        end
        one_str = str(isi);
        %   parse the string. 
        result  = textscan( one_str, '%c%f%f%f%f%f', 'CollectOutput',true ); 
        %   make sure that only results are included in the output
        assert( strcmp( unique(result{1}), 'R' )     ...
            ,   'Non-result rows included in result' )
        out = result{2};
    end
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