How to extract two repeated toggling data from two fixed channel using MATLAB

Hi Friends,
I have a text file looks like below 
Time 20.20
Channel   SVID
01         5
02         7
03         1   
Time  20.40 
same sequence...
Time  20.60
01         1
02         7
03         5  
Time  20.80
01         1
02         7
03         --  
....... 
As you can see in the 3rd time interval my satellite number 1 and 5 swap to channel 
01 and 03. Earlier I was extracting data through channel wise using index method because 
all channel and time will be repeating after particular sequence. But when I was extracting data 
let say through  channel 01 means actually I am taking two satellite id value 5 and 1.But again at time 20.80
satellite 05 is missed. So if I plot accordingly  channel then I can not know what time my satellite 05 became invisible and giving me wrong information 
about that satellite. I want to exactly what time it missed. If at all it is not missed but switching to different channel then how to extract data .
My channel sequence is fixed. 

 I extracted data using 
 fid=fopen('testingGPS.txt','r');
xdata=textscan(fid,'%s','delimiter','\n');
ydata=xdata{1};
zdata=ydata(4:24:end,:);%GPS-Channel-05
kdata=ydata(20:24:end,:);%SBAS-Channel-01

 But as I said my plot giving me wrong information.
 No logic is working at this moment.
 Any help is highly appreciated
 Thanks 
 POKA

Answer 1

[fbaillon]

If I understand your question correctly, you can write something like that:

fid=fopen('testingGPS.txt.txt','r');
xdata=textscan(fid,'%s','delimiter','\n');
ydata=xdata{1};
ydata=cellfun(@(x) strrep(x,'--','0'),ydata,'UniformOutput',false);
iD=1;
for iL=2:4:length(ydata)
    zdata(iD,:)=sscanf(ydata{iL},'%d %d');%GPS-Channel-05
    kdata(iD,:)=sscanf(ydata{iL+2},'%d %d');%SBAS-Channel-01
    iD=iD+1;
end
fclose(fid);
%
zdata=zdata(:,2);
kdata=kdata(:,2);
%

[POKA]

 Thanks for responding.
 I will check .  I will utilize your suggestion.

[POKA]

 Hi,
 It is showing error 
 Subscripted assignment dimension mismatch in the line .
 zdata(iD,:)=sscanf(ydata{iL},'%d %d')

 % In short I want to say that ,let say there are 3 channel and 
  3 inputs are there.Inp-1,inp-2,inp-3. These inputs are coming through these 
3 channel at particular time. Now these input may change their channel at 
different time.Again input may not coming to channel during any time.
Now I want to check whether (say inp-1 corresponding to sv id) was present 
throughout the test time. No matter in which channel appears.
 At the same time in which time input was not appearing. So I want to extract only input 
1 from these channel and plot them over time.
Hope my sentences makes some meaning now.