Using sscanf and NaN

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Sebastian Ciuban 2014-6-6

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评论： Geoff Hayes 2014-6-9

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Greetings,

So if i have the following:

a = '21414839.260   112535757.19909      2294.184    21414838.320    87690207.10148 1787.672'

Using:

A=sscanf(a,'%f')

Will return:

But if If the last 3 numbers are missing from the line :

a = '21414839.260   112535757.19909      2294.184                                        '

I want this to be returned:

 A =
     1.0e+08 *
      0.2141
      1.1254
      0.0000
      NaN
      NaN
      NaN

How can I make this possible?

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Geoff Hayes 2014-6-6

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If you know that sscanf of the input string is to return 6 numbers, and A is only populated with three, then you could do the following

A = [A; repmat(NaN,6-length(A),1)];

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Geoff Hayes 2014-6-9

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Hi Ciuban - the problem is that A matrix that is being populated with the satellite information is not being reset/cleared for each block:

 while ~feof(fid)
   % do some stuff
   [~,n]=size(index); 
   for i=1:n
     A(1,i)=str2num(….
     % etc.

So once this matrix reaches size 12 (for whatever iteration of the while loop) then it holds on to that excess data for each subsequent block that has less than 12 satellites. When the last block of eight satellites is evaluated, A keeps the last four from some previous block(s). To get around this, just re-size the A matrix prior to entering the for loop since you know how many rows (7) and you know the columns (n):

while ~feof(fid)
    tline = fgets(fid);
    sat=tline;
    index=strfind(tline,'G'); 
    [~,n]=size(index); 
    A = zeros(7,n);  % add this line !!!!
    for i=1:n
       % etc.

Pre-allocation of a matrix is usually a good idea - it prevents a matrix from being resized on subsequent iterations (may improve speed), and clears those pesky warnings in the editor.

Also, don't forget to add in the fclose(fid); statement. Hope the above helps!

Sebastian Ciuban 2014-6-9