Conditional text import or import by header name - MATLAB

Question

Is there a way to perform conditional text import within MATLAB? e.g. with a tab-delimited .txt file in this format:

Type    A   B   C   D   E
 A    5000  2   5   16  19
 A    5000  3   4   5   4
 A    5000  4   1   4   5
 B    500   19  8   2   7
 B    500   18  9   8   1
 B    500   2   9   13  2
 B    100   3   10  15  9
 B    5000  4   15  14  10

Is there a method to import only those lines where Column A contains '5000'?

This is preferential over importing the entire .txt file and separating the data afterward as in reality, my text files are rather large (~200MB each) - but if there is a way to do this quickly, that would also be a suitable solution.

Alternatively, is there a method (similar to R) where you can import and handle data using the headers contained in the .txt file? e.g. importing 'Type' 'A' 'B' and 'D' whilst ignoring 'C' and 'E' in the above example. This is needed if the input file is flexible in format with additional columns added sometimes meaning their relative positions change.

Answer 1

You might try reading the input file line by line, check if the line contains the reference value (5000 in this case) in the reference column (column 2 in this case).

If so you can store the input, otherwise, you discard it.

In the following code, based on your template, you can define the reference value and the reference column at the beginning of the code.

You can then convert cellarray output to array

% Define the column index
col_idx=2
% Define the reference value
ref_value=5000
% Open input file
fid=fopen('in.txt');
% Read header
tline = fgetl(fid);
% Initialize conter
cnt=0;
% Initialize output variable
data=[];
% Read the file line by line
while 1
   % Read the line
   tline = fgetl(fid);
   % Check for the end of file
   if ~ischar(tline)
      break
   end
   % Get the line field
   c=textscan(tline,'%c%f%f%f%f%f')
   % If the seconf field contains the ref value, then store the inout data
   if(c{col_idx} == ref_value)
      data=[data;c]
   end
end
fclose(fid);
% Convert cell 2 array
c=data(:,2:end)
num_data=cell2mat(c)
% Convert first column to char
lab=char(data(:,1))

Hope this helps.