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Java

Nancy Melucci
PLUS
Nancy Melucci
Courses Plus Student 36,159 Points
Posted by Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points

Regex for complex numbers (Java)

I have a regex that recognizes most complex number cases but makes a couple of serious mistakes

1) it identifies "i" and "-i" as having 0.0 coefficient

2) it calls "not a match" for numbers of this format

real number + i real number - i

here is my regex (below)

do you know how I can tweak is so it will handle all complex and imaginary numbers including those that involve an i that has a 1 or - 1 coefficient (therefore, -i or i)

hope I made that clear....

Nancy M.

Pattern p =  Pattern.compile("(?<real>-?\\d*[.]?\\d+)??((?<imag>[+-]?\\d*[.]?\\d+)i|i|-i)?$");
Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points
Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points

Update:

I figured out how to get it to recognize i and -i by using a switch case. I still cannot figure out how to make regex work for expressions such as "2+i" and "2-i"....here is what I have which works for everything except a real numbers combined with i and - i.

 Pattern p =  Pattern.compile("(?<real>-?\\d*[.]?\\d+)??((?<imag>[+-]?\\d*[.]?\\d+)i|i|-i|\\d+[+-]i"
             + ")?$|(?<imagOnly>^[-+]i|-i\\d*\\?\\d*i$)[-]i|i$(?<realimag>^\\d+[+-]i$)");


        Matcher m = p.matcher(word);
      try{
        if(m.matches() ) {      
       //try{
       String r = m.group("real");
       String i = m.group("imag");
       String io = m.group("imagOnly");
       String rio = m.group("realimag");
       real = (r != (String)null? Double.parseDouble(r): 0);
       imag = (i != (String)null? Double.parseDouble(i): 0);
       imagOnly = (io != (String)null? Double.parseDouble(io): 0);
       realimag = (rio != (String)null? Double.parseDouble(rio): 0);
       try{
       switch (word) {        
           case "-i":
           imag = -1.0;                        
           break;
           case "+i":
           imag = 1.0; 
           break;
           case "i":
           imag = 1.0; 
           break;
           case "\\d+[+-]i":
           realimag = (rio != (String)null? Double.parseDouble(rio): 0);
           break;
           default:
           imagOnly = (io != (String)null? Double.parseDouble(io): 0);
       }
       }catch(InputMismatchException ime){
          System.out.println("Wrong format");

       }     
               System.out.println("Real: " + real + "," + "\timag: " + imag);
       }else{ System.out.println("Not a match");

        } 
           } catch (InputMismatchException ime){
          System.out.println("Wrong format");

Just so you know I really am struggling with this and not just trying to get free help...

thanks everyone

3 Answers

Craig Dennis
STAFF
Craig Dennis
Treehouse Teacher
Craig Dennis
Craig Dennis
Treehouse Teacher

Hi Nancy!

Fun problem! What about using a library like Apache Commons Math? Would this parse method do the trick?

Can you use an external lib?

Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points
Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points

I will check out the library/method. I am very very very slow at this. So, I appreciate your patience and help. It is fun. Tough fun. I'll keep you posted.

Nancy M.

Nancy Melucci
PLUS
Nancy Melucci
Courses Plus Student 36,159 Points
Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points

Update: Per Regexr (http://regexr.com/) I have the correct regex for the cases such as

2+i

-66+i

7-i

It's /[-1-9][0-9]+[+-]i/

It isn't working in my switch statement though... I'll keep working on it.

Nancy

Nancy Melucci
PLUS
Nancy Melucci
Courses Plus Student 36,159 Points
Nancy Melucci
Nancy Melucci
Courses Plus Student 36,159 Points

Update:

I got some help from the professor last week. I am sure he was trying to help me when he rearranged my code and encouraged me to try again but now it works worse and I am even more lost trying to get it to run all the complex and imaginary cases correctly. I can't even get it back to where I had it last week.

This is the array of data I am running:

String[] data = {"i", "-i", "2+i", "-2+i", "2-i", "-2+i", "2+2i", "2-2i", "2i", "-2i", "splunge"};

Here is what it gives me back in the output:

run: Real: 0.0, imag: 1.0

Real: 0.0, imag: 1.0

Real: 0.0, imag: -1.0

Real: 2.0, imag: -1.0

Real: -2.0, imag: -1.0

Real: 2.0, imag: -1.0

Real: -2.0, imag: -1.0

Real: 2.0, imag: -1.0

Real: 2.0, imag: -1.0

Real: 0.0, imag: -1.0

Real: 0.0, imag: -1.0

Not a match

BUILD SUCCESSFUL (total time: 25 seconds)

The code follows. I don't know how else to learn exactly what the regex means without getting someone to tell me why all my i's are being identified as having coefficients of negative 1 and why this runs worse than what I had. I should have saved my version before letting him rearrange it. >< The rest of the class is going to be 5 program ahead of me soon. Despair.

public class ComplexTrialRun {

    private double real;
    private double imag;


    public static void main(String [] args){



      String[] data = {"i", "-i", "2+i", "-2+i", "2-i", "-2+i", "2+2i", "2-2i", "2i", "-2i", "splunge"};
        int i = 0;
     ComplexTrialRun c = new ComplexTrialRun();    
      ComplexTrialRun result = c.setComplex(data[i]);
          for(i = 0; i<data.length; i++){
         c.setComplex(data[i]);

          }
    }

    public ComplexTrialRun setComplex( String word)
        {


     Pattern p =  Pattern.compile("(?<real>-?\\d*[.]?\\d+)??(?<imag>[+-]?\\d*[.]?\\d*i)|"
            +"(?<imagOnly>^[-+]i|-i\\d*\\?\\d*i$)[-]i|i$(?<realimag>^\\d+[-]i$)");

        Matcher m = p.matcher(word);

        if(m.find() ) {      
       //try{
       String r = m.group("real");
       String i = m.group("imag");
          //"i", "-i", "2+i", "-2+i", "2-i", "-2+i", "2+2i", "2-2i", "2i", "-2i", "splunge"
       real = (r != (String)null? Double.parseDouble(r): 0); 
       try{
       if (i==null){    
             real = (r != (String)null? Double.parseDouble(r): 0); 
       }else {
           switch (word) {        
           case "i":
           imag = 1.0;                        
           break;
           case "-i":
           imag = -1.0;                        
           break;    
           case "[-1-9][1-9]+[-]i$":
           real = (r != (String)null? Double.parseDouble(r): 0);
           imag = 1.0;
           break;
           case "[-1-9][1-9]+[+]i$":
           real = (r != (String)null? Double.parseDouble(r): 0);
           imag = -1.0;
            break;
           case "[-1-9][1-9]i+[+-]i$":
           real = (r != (String)null? Double.parseDouble(r): 0);
           imag = 1.0;
           System.out.println("This also sucks!");    
           break;

       }


       } 
       }catch(InputMismatchException ime){
          System.out.println("Wrong format");

        // i = m.group("imagOnly"); 
       imag = (i != (String)null? Double.parseDouble(i): 0); //try and catch i


       }     
               System.out.println("Real: " + real + "," + "\timag: " + imag);
       }else{ System.out.println("Not a match");

        } 


        return this;
}
}