Using sscanf (or equivalent) to extract double from string.

Let's say I have a string as follows:

   string = '2.3A 4B C'

I want to apply a function that will output the following:

   [2.3 4 1]

where these values are simply the "prefixes" (converted to doubles) of the letters specified within the string. One important note is that any letter lacking a prefix should output a 1.

My first thought was to use sscanf and include some condition for letters lacking prefixes, but it hasn't quite worked the way I'd like.

Any suggestions from the Matlab world?

Thanks!

Answer 1

[Stephen23]

This solution uses regexp to detect the sequences of characters (possibly with leading digits and optional decimal fraction). It returns the numeric parts, which are then converted to floating point numbers. Any empty cells are given the value 1, then the whole thing is converted to a numeric array.

>> str = '2.3A 4B C';
>> A = regexp(str,'(\d+(\.\d+)?)?[A-Z]+','tokens');
>> A = [A{:}];
>> A = cellfun(@str2num,A,'UniformOutput',false);
>> A{cellfun('isempty',A)} = 1;
>> A = [A{:}]
A =
          2.3            4            1

No loops, no cluttering up of the workspace... elegance is never overrated!

Answer 2

[James]

Well, this seems to work. Elegance is overrated, right? aha

 name = '2.3A 4B C';

 letterIndex = regexp(name,'[A-Z]');

 letterNum = 1;
 floatLength = 0;
 outVal = zeros(1,length(letterIndex));

 for i = 1:length(name)

   if i == letterIndex(letterNum)
       if floatLength == 1
          outVal(letterNum) = 1;
       else
           outVal(letterNum) = str2double(name((i-floatLength):(i-1)));
       end
       floatLength = 0;
       letterNum = letterNum + 1;
   else
       floatLength = floatLength + 1;
   end

 end