Converting Letters to Corresponding Numbers

[jason candelora]

Hi,
I am workin on an excercise where I am converting phone numbers with letters and converting them to plain phone numbers with all numbers. The code I am using is very bulky and is as follows:
wordToConvert = input.replace('a', '2');
wordToConvert = wordToConvert.replace('b', '2');
wordToConvert = wordToConvert.replace('c', '2');
wordToConvert = wordToConvert.replace('d', '3');
wordToConvert = wordToConvert.replace('e', '3');
wordToConvert = wordToConvert.replace('f', '3');
wordToConvert = wordToConvert.replace('g', '4');
wordToConvert = wordToConvert.replace('h', '4');
wordToConvert = wordToConvert.replace('i', '4');
wordToConvert = wordToConvert.replace('j', '5');
wordToConvert = wordToConvert.replace('k', '5');
wordToConvert = wordToConvert.replace('l', '5');
wordToConvert = wordToConvert.replace('m', '6');
wordToConvert = wordToConvert.replace('n', '6');
wordToConvert = wordToConvert.replace('o', '6');
wordToConvert = wordToConvert.replace('p', '7');
wordToConvert = wordToConvert.replace('q', '7');
wordToConvert = wordToConvert.replace('r', '7');
wordToConvert = wordToConvert.replace('s', '7');
wordToConvert = wordToConvert.replace('t', '8');
wordToConvert = wordToConvert.replace('u', '8');
wordToConvert = wordToConvert.replace('v', '8');
wordToConvert = wordToConvert.replace('w', '9');
wordToConvert = wordToConvert.replace('x', '9');
wordToConvert = wordToConvert.replace('y', '9');
wordToConvert = wordToConvert.replace('z', '9');
wordToConvert = wordToConvert.replace('A', '2');
wordToConvert = wordToConvert.replace('B', '2');
wordToConvert = wordToConvert.replace('C', '2');
wordToConvert = wordToConvert.replace('D', '3');
wordToConvert = wordToConvert.replace('E', '3');
wordToConvert = wordToConvert.replace('F', '3');
wordToConvert = wordToConvert.replace('G', '4');
wordToConvert = wordToConvert.replace('H', '4');
wordToConvert = wordToConvert.replace('I', '4');
wordToConvert = wordToConvert.replace('J', '5');
wordToConvert = wordToConvert.replace('K', '5');
wordToConvert = wordToConvert.replace('L', '5');
wordToConvert = wordToConvert.replace('M', '6');
wordToConvert = wordToConvert.replace('N', '6');
wordToConvert = wordToConvert.replace('O', '6');
wordToConvert = wordToConvert.replace('P', '7');
wordToConvert = wordToConvert.replace('Q', '7');
wordToConvert = wordToConvert.replace('R', '7');
wordToConvert = wordToConvert.replace('S', '7');
wordToConvert = wordToConvert.replace('T', '8');
wordToConvert = wordToConvert.replace('U', '8');
wordToConvert = wordToConvert.replace('V', '8');
wordToConvert = wordToConvert.replace('W', '9');
wordToConvert = wordToConvert.replace('X', '9');
wordToConvert = wordToConvert.replace('Y', '9');
wordToConvert = wordToConvert.replace('Z', '9');

Is there a more compact way to do this??
Thanks for any help!
Jason

[Joel McNary]

Yes, that is bulky. What you might want to do is set up a Hash to handle this for you. Also, you can use regualr expressions to slim down the code a bit.

        //Start with a pizza place in Cambridge
        //known to some as "Satan Surprise,"
        //because of its phone number.
        String phoneNumber = "666-HAHA";
        java.util.Map aMap = new java.util.HashMap();
        aMap.put("[a-c]", "2");
        aMap.put("[d-f]", "3");
        aMap.put("[g-i]", "4");
        aMap.put("[j-l]", "5");
        aMap.put("[m-o]", "6");
        aMap.put("[p-s]", "7");
        aMap.put("[t-v]", "8");
        aMap.put("[w-z]", "9");
        phoneNumber = phoneNumber.toLowerCase();
        java.util.Iterator keys = aMap.keySet().iterator();
        while (keys.hasNext()){
            String regex = (String) keys.next();
            String replacementValue = (String) aMap.get(regex);
            phoneNumber = phoneNumber.replaceAll(regex, replacementValue);
        }
        System.out.println(phoneNumber);

This print out 666-4242.

[Ernest Friedman-Hill]

Hi Jason,
Welcome to JavaRanch!
Wow. Yeah, that's not the most efficient way to do things, because each "replace" is allocating a whole new string and copying all the data over.
I'd do this using a lookup table, since the translation is slightly irregular, something like

char[] digits = {
   2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9
};
char[] data = input.toCharArray();
for (int i=0; i<data.length; ++i) {
   char c = data[i];
   c = Character.toUpperCase(c);
   if (c >= 'A' && c <= 'Z')
       data[i] = digits[c-'A'];
}
return new String(data);

I'd test this code thoroughly before using it, as I just made it up off the top of my head. Note I used the explicit less-than/greater-than tests instead of Character.isLetter() so that non-ASCII letters simply wouldn't be converted; you might want to detect these and throw an exception of something.

[Joel McNary]

Or...

        StringBuffer aBuffer = new StringBuffer("666-HAHA".toLowerCase());
        int count = aBuffer.length();
        for (int index = 0; index < count; index++){
            char aChar = aBuffer.charAt(index);
            if ((aChar >= 'a') && (aChar <= 'z')){
                if (aChar > 'w'){
                    aChar -= 2;
                }
                else if (aChar > 'p'){
                    --aChar;
                }
                aChar -='a';
aChar = (char)(aChar / 3);
                aChar += '2';
                aBuffer.setCharAt(index, aChar);
            }
        }
        System.out.println(aBuffer.toString());

will also work.

[Joel McNary]

Originally posted by Ernest Friedman-Hill:

char[] digits = {
   2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9
};

Don't forget that you'd need single quotes around all of those digits: '2', '2', '2', etc. Otherwise you'd get some strangeness as the output.

[Ernest Friedman-Hill]

Yep, you're sure right. See, I said to test very carefully!

[jason candelora]

Thanks very much for all of your replys!
I will try some of this code later....
Jason

[Thomas Paul]

Originally posted by Ernest Friedman-Hill:
Wow. Yeah, that's not the most efficient way to do things, because each "replace" is allocating a whole new string and copying all the data over.

Thankfully, it isn't quite as bad as that! If nothing is replaced then the original String is returned and no new String is created. So at worst we are creating six extra Strings that we didn't need.
You will get no argument from me as to the inefficiency of running all those replace methods though!
Another way to do it would be to convert the String into a char array and then use a switch statement to change the characters. No specific advantage to this. Just one more way to do the same thing.

public class LettersToNums {
    public static void main(String[] args) {
        char[] data = "666-HAHA".toCharArray();
        for (int i=0; i<data.length; ++i) {
            char c = data[i];
            c = Character.toLowerCase(c);
            switch (c) {
                case 'a':
                case 'b':
                case 'c':   data[i] = '2';
                            break;
                case 'd':
                case 'e':
                case 'f':   data[i] = '3';
                            break;
                case 'g':
                case 'h':
                case 'i':   data[i] = '4';
                            break;
                case 'j':
                case 'k':
                case 'l':   data[i] = '5';
                            break;
                case 'm':
                case 'n':
                case 'o':   data[i] = '6';
                            break;
                case 'p':
                case 'q':
                case 'r':
                case 's':   data[i] = '7';
                            break;
                case 't':
                case 'u':
                case 'v':   data[i] = '8';
                            break;
                case 'w':
                case 'x':
                case 'y':
                case 'z':   data[i] = '9';
            }
        }
        System.out.println(new String(data));
    }
}

[David Koontz]

Perhaps my solution is not as effecient, however...
Just submitted a class TelephoneNumber to do phone formating to
SourceForge
http://sourceforge.net/snippet/detail.php?type=snippet&id=101225
The TelephoneNumber class represents a US telephone number.
This class contains many constructors for various uses. It then stores the telephone number internally in seperate codes (area code, exchange, etc.). This encourages
use of the format method to output the telephone number in any style the programmer wishes.
[needs i18n work]
Example usage:
long number = 8005551212L;
TelephoneNumber phone = new TelephoneNumber(number);
StringBuffer msg = new StringBuffer("Call me at ");
msg.append(phone.format());
// msg is now "Call me at [phone]"

[David Koontz]

Oh - it handles this:
n = new TelephoneNumber("(888) HOLY COW");
out.println(n.format());
prints the #s or alpha & #s
David