Can I speed up this text file parsing code?

I am reading in a large text files (~4MB) containing one column of of different readings. The part of my code that sorts the column of 5 reading types in to 5 different vectors is taking ~2 minutes to run. Is there a code change I can make to speed this up?

fid=fopen(fileName);

    C = textscan(fid, '%f');

    rawData=cell2mat(C);
    toc
    j=1;
    k=1;
    display('parsing data');tic
    speed=[];voltage=[];current=[];force=[];displacement=[];
    while  j<=length(rawData) 

        displacement(k)=rawData(j);
        force(k)=rawData(j+1);
        current(k)=rawData(j+2) ;
        voltage(k)=rawData(j+3);
        speed(k)=rawData(j+4);

        j=j+5;
        k=k+1;
    end

    fclose(fid);

Answer 1

[Jan]

Or try FSCANF instead:

    Data = fscanf(fid, '%f', Inf);
    fclose(fid);

    len = numel(Data);
    displacement = Data(1:5:len);
    force        = Data(2:5:len);
    current      = Data(3:5:len);
    voltage      = Data(4:5:len);
    speed        = Data(5:5:len);

[Mark]

I have never used the "1:5:len" format in this way. Simple and effective. Thanks!

Answer 2

[Sean de Wolski]

Preallocate, preallocate, preallocate!!!!!!! (just like m-lint (the orange squiggly line) is telling you)

v = 1:5:length(rawdata);
n = length(v);
force = zeros(n,1);
displacement = zeros(n,1);
current = zeros(n,1);
voltage = zeros(n,1);
speed = zeros(n,1);

for jj = v
      displacement(k)=rawData(jj);
      force(k)=rawData(jj+1);
      current(k)=rawData(jj+2) ;
      voltage(k)=rawData(jj+3);
      speed(k)=rawData(jj+4);
      k=k+1;
end

or even better just use reshape:

rawData = reshape(rawData,[],5)';
displacement = rawData(:,1);
force = rawData(:,2);
current = rawData(:,3);
voltage = rawData(:,4);
speed = rawData(:,5);

[Mark]

Sean de,

Thank you for responding so quickly. I tried preallocating using cell, but I get "Maximum variable size allowed by the program is exceeded."

the reshape function doesn't seem to work for my format "described below"

a

b

c

d

e

a

b

c

d

e

.

.

.

to

voltage=a,a,...

current=b,b,...

.

.

.

[Sean de Wolski]

There's no reason for cells since all data is the same size. The reshape command will give you an nx5 matrix where each column is what you want...

[Sean de Wolski]

Jan's way is more effective anyway though!