How can I extract a single value from every 86 lines of a long text file?

The file repeats every 86 lines. I am trying to extract every 86th row, starting with row 1. I am attaching a small section of the text file below, and my attempt below that. The full file is 39904 lines long with a total of 39904/86=464 numbers to extract.

               58.53              185.05             179.93                 0.00              192.17               192.17
               58.58              127.17             113.18                 0.00              128.08               128.08
               58.64              121.15             107.12                 0.00              121.93               121.93
               58.69              117.62             103.56                 0.00              118.29               118.29
               58.75              115.12             101.02                 0.00              115.68               115.68
               58.80              113.18              99.05                 0.00              113.64               113.64
               58.86              111.59              97.43                 0.00              111.96               111.96
               58.91              110.25              96.06                 0.00              110.53               110.53
               58.96              109.09              94.86                 0.00              109.28               109.28
               59.02              108.06              93.81                 0.00              108.17               108.17
               59.51              102.03              87.58                 0.00              101.57               101.57

                                                  SUMMED 1/3 OCTAVE BAND SPECTRA

                      OBSERVER    2 LOCATED AT X=   40731.000         Y=   0.0000000         Z=   17996.158    

 FREQUENCIES     0.50000E+02   0.63000E+02   0.80000E+02   0.10000E+03   0.12500E+03   0.16000E+03   0.20000E+03   0.25000E+03
                 0.31500E+03   0.40000E+03   0.50000E+03   0.63000E+03   0.80000E+03   0.10000E+04   0.12500E+04   0.16000E+04
                 0.20000E+04   0.25000E+04   0.31500E+04   0.40000E+04   0.50000E+04   0.63000E+04   0.80000E+04   0.10000E+05


 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.53 SPL         150.67        152.00        153.15        154.07        154.94        155.97        156.81        157.54
          SPL         158.13        158.37        158.20        157.64        156.80        155.83        154.54        152.98
          SPL         151.85        150.14        148.67        147.31        145.89        144.71        144.27        146.16

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.58 SPL         118.48        119.38        119.91        119.37        118.28        116.32        114.21        112.08
          SPL         109.85        107.47        105.31        103.15        101.01         99.13         98.28         95.48
          SPL          93.74         92.44         89.93         88.09         85.99         83.98         82.30         81.38

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.64 SPL         112.47        113.37        113.90        113.36        112.27        110.31        108.20        106.07
          SPL         103.83        101.45         99.28         97.10         94.94         93.03         92.13         89.26
          SPL          87.43         86.01         83.33         81.26         78.90         76.48         74.36         73.07

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.69 SPL         108.95        109.85        110.38        109.84        108.75        106.79        104.68        102.55
          SPL         100.30         97.91         95.73         93.54         91.36         89.42         88.48         85.54
          SPL          83.62         82.07         79.23         76.92         74.29         71.47         68.92         67.26

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.75 SPL         106.45        107.35        107.88        107.34        106.25        104.29        102.18        100.04
          SPL          97.80         95.40         93.21         91.01         88.80         86.83         85.84         82.84
          SPL          80.83         79.16         76.15         73.61         70.71         67.49         64.49         62.47

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.80 SPL         104.51        105.42        105.94        105.40        104.31        102.35        100.24         98.10
          SPL          95.85         93.45         91.25         89.03         86.80         84.80         83.77         80.69
          SPL          78.59         76.81         73.62         70.85         67.69         64.08         60.63         58.24

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.86 SPL         102.93        103.83        104.36        103.82        102.72        100.76         98.65         96.51
          SPL          94.26         91.85         89.65         87.41         85.16         83.13         82.05         78.90
          SPL          76.71         74.81         71.46         68.45         65.03         61.02         57.13         54.37

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.91 SPL         101.59        102.49        103.02        102.48        101.38         99.42         97.31         95.17
          SPL          92.91         90.50         88.28         86.03         83.76         81.69         80.58         77.36
          SPL          75.08         73.05         69.53         66.30         62.61         58.21         53.88         50.75

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    58.96 SPL         100.43        101.33        101.86        101.32        100.22         98.26         96.14         94.00
          SPL          91.74         89.32         87.10         84.84         82.54         80.44         79.28         75.99
          SPL          73.62         71.48         67.79         64.32         60.37         55.58         50.81         47.31

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    59.02 SPL          99.40        100.31        100.83        100.29         99.20         97.23         95.12         92.97
          SPL          90.71         88.28         86.05         83.78         81.46         79.33         78.12         74.77
          SPL          72.30         70.04         66.19         62.49         58.28         53.10         47.87         44.01

 OBS. TIME                                     SOUND PRESSURE LEVEL (SPL) FOR EACH FREQUENCY
    59.51 SPL          93.40         94.30         94.82         94.28         93.18         91.21         89.08         86.92
          SPL          84.63         82.15         79.84         77.43         74.91         72.50         70.91         66.93
          SPL          63.67         60.34         55.00         49.26         42.73         34.12         24.91         17.70

                                    TIME HISTORIES OF THE NOISE LEVELS AT THE OBSERVER POSITIONS 
                                              ( 0.00 MEANS VALUE WAS NOT COMPUTED )

                             OBSERVER     2   (   40731.000         0.0000000         17996.158      )

              OBSERVER            OVERALL           A-WEIGHTED           D-WEIGHTED        PERCEIVED NOISE      TONE-CORRECTED
                TIME                SPL                 SPL                  SPL             LEVEL (PNL)          PNL (PNLT)
                                   (DB)               (DB(A))              (DB(D))             (PNDB)               (PNDB)
 ------------------------------------------------------------------------------------------------------------------------------

               58.53              168.41             165.04                 0.00              177.10               177.10

My attempt:

               
close all; clc; clear all;

fid = fopen("fort18000.txt",'r');

for j = 1:464
data(j,:) = textscan(fid,'%f %f %f %f %f %f /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n /n');
end

My understanding is that the 86 /n specifiers should skip 86 lines after line 1, then the loop will repeat. However, my results from this provide all of the first 11 rows from the text file and nothing else. I've been stumped by this for a while. Any advice?

[per isakson]

The content that you have included in your question contains 87 lines

Is it this line and corresponding lines in the following blocks that you want to retrieve?

58.53              185.05             179.93                 0.00              192.17               192.17

[Stephen Willoughby]

Thanks for the comment. I want every 86th line starting at line 1. So thats line 1, 87, 173 (not shown above), ..., 39904. So ultimately what I'm looking for is:

58.53              185.05             179.93                 0.00              192.17               192.17
58.53              168.41             165.04                 0.00              177.10               177.10
.
.
.

Answer 1

[per isakson]

Try this

%% Read all lines as text
fid = fopen( 'fort18000.txt' );
cac = textscan( fid, '%s', 'Delimiter','\n' );
[~] = fclose( fid );
cac = cac{1};
%% Parse every N:th line
N   = 86;
len = length(cac);
out = nan( len/N, 6 );
kk  = 0;
for jj = 1 : N : len
    buf = textscan( cac{jj}, '%f%f%f%f%f%f' );
    kk = kk +1;
    out(kk,:) = [buf{:}];
end

[Stephen Willoughby]

This worked perfectly. Thank you so much!