Copy text from a string that meets a certain condition MATLAB

Question

i have a strings from a text file:

20130806_083642832,!AIVDM,1,1,,B,13aFeA0P00PEqQNNC4Um7Ow`2@O2,0*5E

20130806_083643032,!AIVDM,2,1,4,B,E>jN6<0W6@1WPab3bPa2@LtP0000:uoH?9Ur,0*50

i need to go through the characters and extract the date at the start then the message that starts after B, (but could also be A,) up until ,0

Any thoughts?

Answer 1

Ok, there are much more elegant ways to solve this, but my following example will give you a feeling on how to manipulate strings in MatLab (Which might be the thing you are having problems with). Here you go:

String='20130806_083642832,!AIVDM,1,1,,B,13aFeA0P00PEqQNNC4Um7Ow`2@O2,0*5E'

for i=1:length(String)
   if(strcmp(String(i),'B'))     %or strcmp(String(i),'A')
       for j=i:length(String)    %or "for j=length(String):i" if you meant the last 0 ;) 
           if(strcmp(String(j),'0'))

               String2=String(i:j)

               break
           end
       end
       break
   end
end

Output

String =

20130806_083642832,!AIVDM,1,1,,B,13aFeA0P00PEqQNNC4Um7Ow`2@O2,0*5E


String2 =

B,13aFeA0

Just play around with string indexing and with strcmp or strcmpi and you'll get a feeling and will be able to write much nicer expressions.

Now try extracting the date by yourself!

Hope that helps!

Answer 2

Without loops you could do something like this:

startString = ['20130806_083642832,!AIVDM,1,1,,B,13aFeA0P00PEqQNNC4Um7Ow`2@O2,0*5E'];
startPosition = find(startString == 'B') + 1;
if ~startPosition
    startPosition = find(startString == 'A') + 1;
end
tmpMessage = startString(startPosition:end);

endPosition = find(tmpMessage == '0') - 1;
outMessage = tmpMessage(1:endPosition(1))

dateString = startString(1:8)

This gives the output:

outMessage = ,13aFeA
dateString = 20130806