MATLAB: Extracting column and specific sorted row data from a large text file

specific column and rowtext file import

Hello everybody,
I have a large text file of 4Gb. I wanted to import the file into MATLAB and extract certain column and row.
It is required to extract the data corresponding to Time=86400. For e.g., Line 5 should be skipped and Line 17 should be included.
In Line 17, the cell number (1) and slope angle (14.6) along with Z corresponding to the lowest positive value of P (in several cases, a set of both positive and negative values of P are seen) should be selected.
I have attached a sample file.
The final output will look like:
Cell_number Slope_Angle Z P
1 14.6 0.10000E-02 0.93631E-03
2 14.4 0.10000E-02 0.93631E-03
Thanks a lot !!

Best Answer

[EDIT]
f = fopen('FILE_MATLAB.txt');
c = textscan(f,'%s','delimiter','\n');
fclose(f);
c = c{:};
cw = c(find(~cellfun(@isempty,regexp(c,'86400.000'))) + (0:11))';
d = regexp(cw,'-?\d+(\.\d+)?(E[+-]\d+)?','match');
N = cell2mat(cellfun(@(x)str2double(x(1:2)),d,'un',0));
[m,n] = size(N);
D = N(2:end,2:2:end);
D(D < 0) = nan;
[~,ii] = min(D);
out = reshape(permute(reshape(N([ones(1,n);kron(ii+1,[1 1])] + m*(0:n-1)),2,2,[]),[2,1,3]),4,[])';
OTHER variant (for data from your file FILE_MATLAB.txt) 
f = fopen('FILE_MATLAB.txt');
c0 = textscan(f,repmat('%16.6f ',1,6),'Headerlines',4,'CollectOutput',1);
fclose(f);
c = c0{:};
t = c(:,4)==86400;
ii = (find(t) + (1:11))';
c2 = c(ii + size(c,1));
c2(c2<0) = nan;
[~,jj] = min(c2);
out = [c(t,1:2),c(ii(1,:) + jj - 1,1:2)];
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