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up vote 1 down vote favorite

I'm reading a text file into a 2D array. The first column ( the one I'm sorting on) is almost all Doubles. As you all probably know, it sorts 1.1 1.6 25.6 6.4, how can I fix this?

import java.io.*;
import java.util.*;

public class Sort {

    public static void main(final String[] args) throws FileNotFoundException {
        FileOutputStream out = new FileOutputStream("/Users/evanlivingston/2d.txt");
        PrintStream pout = new PrintStream(out);
        List<String[]> entries = new ArrayList<String[]>();
        Scanner sc = new Scanner(new File("/Users/evanlivingston/dists/0.txt"));
        while (sc.hasNext()) {
            entries.add(new String[] { sc.next(), sc.next()});
        }
        String[][] table = entries.toArray(new String[0][]);

        Arrays.sort(table, new Comparator<String[]>() {
            @Override
            public int compare(String[] s1, String[] s2) {
                String t1 = s1[0];
                String t2 = s2[0];
                return t1.compareTo(t2);               
            }      
        });
        pout.print(java.util.Arrays.deepToString(table));
        pout.close();
    }
}

EDIT:
Here is my updated code. It won't compile.

import java.io.*;
import java.util.*;

public class Sort {
    public static void main(String[] args) throws FileNotFoundException {
        FileOutputStream out = new FileOutputStream("/Users/evanlivingston/2d.txt");
        PrintStream pout = new PrintStream(out);
        List<Coords> coords = new ArrayList<Coords>();
        {
            Scanner sc = new Scanner(new File("/Users/evanlivingston/dists/0.txt"));
            while(sc.hasNextLine()) {
                String[] numstrs = sc.nextLine().split("\\s+");
            }
            String[][] table = coords.toArray(new String[0][]);

            Arrays.sort(table, new Comparator<Double[]>() {
                @Override
                public int compare(Double[] s1, Double[] s2) {
                    double a = Double.parseDouble(s1);
                    double b = Double.parseDouble(s2);
                    compare(a, b);
                }
            });
            pout.print(java.util.Arrays.deepToString(table));
            pout.close();
        }
    }
}
share|improve this question
almost all Doubles? And by "Double" here, I assume you really mean "text that can be interpreted as a floating-point number per the usual conventions, which I wish to sort according to the resulting floating-point value rather than lexicographically". – Karl Knechtel Apr 22 '11 at 5:27
@Karl Knecthel, yes, that's exactly what I mean, I edited to code to be what I assume to be correct, but it wont compile. – evanlivingston Apr 22 '11 at 5:32
1  
it's good that you're editing to follow up, but please add to the original post instead of overwriting. Overwriting removes the context for the original answers, making them look inappropriate for the question. – Lord Torgamus Apr 22 '11 at 5:40
@Lord Torgamus, I'm not sure I can add code without editing my original post as Im limited to 555 characters or so in the comments, is there a way around this? – evanlivingston Apr 22 '11 at 5:51
You're right to want to edit instead of using comments. But you should add the new code separately. It's the difference between "append" and "replace." I edited to your post to illustrate. This works better when you don't change quite so much between versions of the code. – Lord Torgamus Apr 22 '11 at 5:57

4 Answers

up vote 1 down vote

You're comparing String values, not Double values, so 2 comes after 1 and before 6.

To fix this, you should convert your values to actual Double objects with the wrapper method valueOf() (documentation).

EDIT:
I went for the simpler fix above, but camickr's answer is better if you care at all about performance.

Regarding your update not compiling, multiple things are wrong. Did you ever declare a second compare() method anywhere? There's nothing built in for that. Recursively calling the existing compare() won't help in your case.

On that note, you can't call the existing compare(); autoboxing won't convert primitive doubles into arrays of Double objects. And there's no way to parse Double arrays into primitive doubles.

Since you're trying to use primitive doubles now, you could just use the plain old > and < operators to compare with instead of the more complex Comparator stuff.

share|improve this answer
up vote 1 down vote

You're comparing strings, not numeric values. 1 is lexically lower than 2, and 2 is lexically lower than three. So from a string perspective, 234 is less than 3. You have to convert your doubles from strings in order to compare them properly. In Java you do this via:

double aDouble = Double.parseDouble(aString);

so your final expression should really be

double a = Double.parseDouble(firstString);
double b = Double.parseDouble(secondString);
compare(a,b);
share|improve this answer
1  
I was about to upvote this, but the primitive double doesn't have the ability to use the compareTo() method. – Lord Torgamus Apr 22 '11 at 3:16
2  
The link is for a "Double" object. Your code is for a "double" primitive. You can't invoke methods on a primitive. – camickr Apr 22 '11 at 3:44
Really. Try to compile it, see what happens. – Lord Torgamus Apr 22 '11 at 4:06
Ah, you are correct. I meant compare and not compareTo – acconrad Apr 22 '11 at 4:15
show 1 more comment
up vote 6 down vote

Store doubles in the array NOT Strings.

So convert the String to a double when you read it in from your file. Or use the Scanner.nextDouble() method to do this for you.

You don't want to be converting the Strings every time the Comparator is invoked.

share|improve this answer
up vote -1 down vote

Have your comparator convert the strings it is input into doubles and do a numeric comparison rather than a string compare.

That's the advantage of the Comparator concept. It can do anything with the inputs. So if you need to sort Strings as if they were numbers, write a Comparator that'll do just that.

share|improve this answer

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