How do I extract data from a .dat file contain multiple tables?

The example of .dat file is this one . There are various tables for varying RPM of the propellers. I want to be able to extract all the data such that I can make various plots from the data for each RPM.

A direct importdata('PER3_5X5E.dat') puts all the data in one single cell without distributing the data in any manner. This was also the case when I removed all the header text from the .dat file and the file started directly with the RPM value.

Answer 1

[Stephen23]

This reads entire header into cell array hdr, all of the data tables into a cell array out, and the corresponding RPM into a numeric vector rpm. Obviously you can adapt it to your needs.

fnm = 'PER3_105x45.dat';
hdr = {};
fid = fopen(fnm,'rt');
% Read header into cell array:
while ~feof(fid)
  pos = ftell(fid);
  str = strtrim(fgetl(fid));
  if strncmp(str,'PROP RPM',8)
    fseek(fid,pos,'bof');
    break
  else
    hdr{end+1} = str; %#ok<SAGROW>
  end
end
% Read tables into cell array:
out = {};
rpm = [];
fmt = repmat('%f',1,8);
hmt = repmat('%s',1,8);
opt = {'HeaderLines',3, 'MultipleDelimsAsOne',true, 'CollectOutput',true};
while ~feof(fid)
  % Read PROP RPM:
  rpm(end+1) = fscanf(fid,' PROP RPM = %d'); %#ok<SAGROW>
  % Read table of data:
  C = textscan(fid,fmt,opt{:});
  out(end+1) = C(1); %#ok<SAGROW>
end
fclose(fid);

Where the k-th table in out corresponds the k-th RPM in the vector rpm. For example:

>> rpm
rpm =
  Columns 1 through 8
        1000        2000        3000        4000        5000        6000        7000        8000
  Columns 9 through 16
        9000       10000       11000       12000       13000       13999       15000       16000
  Columns 17 through 23
       17000       18000       19000       20000       21000       22000       23000
>> out{end} % corresponds to rpm(end)
ans =
          4.9         0.02       0.0248        0.089       0.0763        9.527       26.107       18.226
          9.7         0.04       0.0515       0.0894       0.0739         9.23       25.294       18.313
         14.6         0.06        0.078        0.089       0.0728        9.099       24.933       18.223
         19.5         0.09       0.1073       0.0883       0.0701        8.758       23.999       18.092
         24.3         0.11       0.1387       0.0876       0.0673        8.404       23.028       17.952
         29.2         0.13       0.1725       0.0869       0.0643        8.037       22.022       17.796
         34.1         0.15       0.2095        0.086       0.0612        7.647       20.955       17.625
           39         0.17        0.249       0.0852       0.0583        7.277       19.941       17.446
         43.8         0.19       0.2929       0.0839       0.0549         6.86       18.798       17.195
         48.7         0.21        0.335        0.082       0.0521        6.508       17.835       16.789
         53.6         0.23       0.3747       0.0796       0.0497        6.211       17.021       16.297
         58.4         0.26       0.4094       0.0769        0.048        5.993       16.421       15.744
         63.3         0.28       0.4402       0.0741       0.0466        5.818       15.943       15.171
         68.2          0.3       0.4693       0.0711       0.0452        5.644       15.465        14.57
           73         0.32       0.4975        0.068       0.0436        5.452       14.939       13.924
         77.9         0.34       0.5207       0.0647       0.0424         5.29       14.497       13.259
         82.8         0.36       0.5348       0.0614       0.0416        5.194       14.233       12.584
         87.6         0.38       0.5579       0.0579       0.0398        4.967        13.61       11.855
         92.5          0.4       0.5749       0.0537       0.0378        4.719       12.931       10.997
         97.4         0.43       0.5852       0.0489       0.0356        4.444       12.176       10.013
        102.3         0.45       0.5914       0.0438       0.0331        4.137       11.337        8.973
        107.1         0.47        0.592       0.0386       0.0305        3.816       10.456        7.907
          112         0.49       0.5845       0.0333       0.0279        3.485         9.55        6.821
        116.9         0.51       0.5678       0.0279       0.0252        3.142         8.61        5.724
        121.7         0.53       0.5372       0.0226       0.0223        2.791        7.649        4.619
        126.6         0.55       0.4864       0.0171       0.0195        2.431        6.661        3.502
        131.5         0.57       0.4012       0.0117       0.0167        2.092        5.733        2.394
        136.3          0.6       0.2549       0.0062       0.0144        1.805        4.945        1.265
        141.2         0.62      -0.0155      -0.0003       0.0118        1.474        4.039       -0.061
>>

tested on this file:

Answer 2

[dpb]

Read the full file into character array and then search for the RPM line; that will give you a set of sections within which to interpret the numeric values into cell arrays by RPM.

Did the importdata solution save the RPM values in a cell? If so, looks like you should be able to just find the V==0.0 data to locate the sections similarly as to the text search above and reformat the big cell array into smaller ones. If the RPM data were lost entirely, then you'd need to reconstruct that of course.

Alternatively, just start a loop and fgetl a line at a time and parse it -- throw away what you get until RPM, read it, you then know how many lines to skip to read a section and "rinse and repeat" until feof