Help Searching a 2D Array (Java)

Question

I'm completely lost. I've googled for this problem for possibly 30 minutes now, and I can't find any java specific solutions (or any solutions that crossover into java).

I've tried using the generic two simple for loops for going through each individual String, but it only seems to return results if the search term is in the first column of the array.

    public static String search(String term) {
        String result = "";
        int row = db.bookdb.length;

        for (int i=0; i<db.bookdb.length; i++) {
            for (int j=0; j<4; j++) {
                if (term.equals(db.bookdb[i][j])) {
                     row = i;
                     break;
                }
            }
        }

        if (row == db.bookdb.length) {
            result += "Your search failed to return any results";
        }
        else {
            for (int j=0; j<4; j++) {
                result += db.bookdb[row][j] + "    ";
            }
        }

        return result;
    }

db is the object i'm working with, and bookdb is the 2D array within said object. (and yes, the amount of columns will always be 4)

If there's any additional information you guys need feel free to ask.

Your search isn't broken. I tested it (see below.) My guess is that the input into your bookdb is broken, always putting data in the first column. — corsiKa
– corsiKa, Commented Mar 29, 2011 at 18:17

corsiKa · Accepted Answer · 2011-03-29 18:32:41Z

2

Your search method works fine. I created a class and used your Search method (COPIED AND PASTED, I didn't even change your search) and it works. This leads me to believe the problem is in how you're entering your data.

class Pdeuchler {

    static Pdeuchler db;

    String[][] bookdb;


    public static String search(String term) {
        String result = "";
        int row = db.bookdb.length;

        outer_loop: // CHANGE #1 added a named loop
        for (int i=0; i<db.bookdb.length; i++) {
            for (int j=0; j<4; j++) {
                if (term.equals(db.bookdb[i][j])) {
                     row = i;
                     //break; //REMOVED
                     break outer_loop; // CHANGE #2 breaking to the outer_loop
                }
            }
        }

        if (row == db.bookdb.length) {
            result += "Your search failed to return any results";
        }
        else {
            for (int j=0; j<4; j++) {
                result += db.bookdb[row][j] + "    ";
            }
        }

        return result;
    }

    public static void main(String[] args) {
        db = new Pdeuchler();
        db.bookdb = new String[10][4]; // title, author, publisher, year

        db.bookdb[0] = new String[] {"Awesome Book","Stan","West","2001"};
        db.bookdb[1] = new String[] {"Cool Story","Dan","North","2002"};
        db.bookdb[2] = new String[] {"Brothers","North","North","2003"};
        db.bookdb[3] = new String[] {"Never again!","Bob","West","2004"};
        db.bookdb[4] = new String[] {"Howdy Partner","Stan","South","2005"};
        db.bookdb[5] = new String[] {"What the StackOverflow?","Dan","North","2006"};
        db.bookdb[6] = new String[] {"That's hilarious","Angie","South","2007"};
        db.bookdb[7] = new String[] {"I like pie","Angie","East","2008"};
        db.bookdb[8] = new String[] {"Bob writes a book","Bob","South","2009"};
        db.bookdb[9] = new String[] {"The adverntures of Bob","Bob","North","2010"};

        System.out.println(search("I like pie"));
        System.out.println(search("North"));
        System.out.println(search("Dan"));
    }

}

And the results:

C:\junk>java Pdeuchler
I like pie    Angie    East    2008
The adverntures of Bob    Bob    North    2010
What the StackOverflow?    Dan    North    2006

C:\junk>

and the results with the change:

C:\junk>javac Pdeuchler.java

C:\junk>java Pdeuchler
I like pie    Angie    East    2008
Cool Story    Dan    North    2002
Cool Story    Dan    North    2002

C:\junk>

If we use an advanced search method (which I'm calling search2) we get this:

C:\junk>java Pdeuchler
simple search:
I like pie    Angie    East    2008
Cool Story    Dan    North    2002
Cool Story    Dan    North    2002

advanced search:
I like pie    Angie    East    2008

Cool Story    Dan    North    2002
Brothers    North    North    2003
What the StackOverflow?    Dan    North    2006
The adverntures of Bob    Bob    North    2010

Cool Story    Dan    North    2002
What the StackOverflow?    Dan    North    2006


C:\junk>

Here's the advanced search method:

public static String search2(String term) {
    String result = "";
    int row = db.bookdb.length;

    for (int i=0; i<db.bookdb.length; i++) {
        for (int j=0; j<4; j++) {
            if (term.equals(db.bookdb[i][j])) {
                 row = i;
                 for (int k=0; k<4; k++) {
                     result += db.bookdb[i][k] + "    ";
                 }
                 result += "\n";
                 break; // breaks out of the INNER (j) loop
            }
        }
    }

    if (row == db.bookdb.length) {
        result += "Your search failed to return any results";
    }
    return result;
}

edited Mar 29, 2011 at 18:32

answered Mar 29, 2011 at 18:00

corsiKa

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7 Comments

pdeuchler Over a year ago

I double checked my array and I've got extraneous spaces bracketing the strings. D'oh. Thanks, I appreciate the help.

corsiKa Over a year ago

@pdechuler sure thing. I'm going to make two edits to the code above, and then paste the result. Ask your professor if they're acceptable to use, because some will frown upon it. If he says it's okay, I would use it. If he says it's not okay, I would incorporate iluxa's answer into your loops.

corsiKa Over a year ago

@pdechuler I made the changes. Do you see what it does? As soon as it finds an acceptable match, it gets out of the loop (by breaking the outer_loop.) This means you now find the FIRST result of the array instead of the LAST. So if you find a match on the first result, you don't search the entire array. Another option would be to always search the array and find ALL the matching elements. I'll edit that one in too.

corsiKa Over a year ago

@pdechuler added advanced search

corsiKa Over a year ago

@pdechuler honestly they're just minor tweaks. Your original search method is just fine. When you're looking at beginning Java courses, heh... if it works, it's right. I helped a buddy grade some CS101 assignments when I was still in uni, and... I was amazed. Simply amazed.

|

iluxa · Accepted Answer · 2011-03-29 18:01:33Z

2

your "break" statement breaks out of the inner loop but not outer one. re-write like this:

boolean found = false;

for (int i = 0; i < db.bookdb.length && !found; i ++) {
  for (int j=0; j<4 && !found; j++) {
    if (yourCondition) {
      row = i;
      found = true;
    }
  }
}

answered Mar 29, 2011 at 18:01

iluxa

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3 Comments

corsiKa Over a year ago

The only consequences of that are 1) You search the entire array, so you find the last result, not the first, and 2) You search the entire array so it takes a little longer. It would only make a difference in output where the same term existed multiple times.

corsiKa Over a year ago

I should clarify, that doesn't mean this is isn't decent advice, it just won't solve the OPs problem. I should also point out that you can use a named loop and break out of it. outer_loop: for(int i = 0... and later break outer_loop;

pdeuchler Over a year ago

Thank you for catching that, but it still doesn't fix the bug (as glowcoder pointed out). And speed isn't an issue, at most it will only be searching a 12x4 array of strings composed of less than 20 chars. Also, i'm assuming that there is only one possible result.

Eamorr · Accepted Answer · 2011-03-29 18:01:17Z

0

Are you sure db.bookdb.length isn't always 1?

This might help you:

int[][] matrix = new int[10][30]; System.out.println("Number of rows = " + matrix.length); System.out.println("Number of columns = " + matrix[0].length);

answered Mar 29, 2011 at 18:01

Eamorr

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Comments

lukastymo · Accepted Answer · 2011-03-29 18:16:04Z

0

I'm not sure what your bookdb is type but you can change it

private static int searchTermInArray(String[][] bookdb, String term) {
    for (int i=0; i<bookdb.length; i++) {
        for (int j=0; j<4; j++) {
            if (term.equals(bookdb[i][j])) {
                return i;
            }
        }
    }
    return -1;
}

public static String search(String term) {
    String result = "";
    int row = searchTermInArray(db.bookdb, term);
    if (row == -1) {
        result += "Your search failed to return any results";
    }
    else {
        for (int j=0; j<4; j++) {
            result += db.bookdb[row][j] + "    ";
        }
    }

    return result;
}

answered Mar 29, 2011 at 18:16

lukastymo

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Comments

Devin Burke · Accepted Answer · 2011-12-12 01:56:54Z

0

You need to break out of both the loops. You can label the outer loop with say "mainfor" and use that label after the break

public static String search(String term) {
    String result = "";
    int row = db.bookdb.length;

    mainfor: for (int i=0; i<db.bookdb.length; i++) {
        for (int j=0; j<4; j++) {
            if (term.equals(db.bookdb[i][j])) {
                 row = i;
                 break mainfor;
            }
        }
    }
 ... //rest of your code as is
}

edited Dec 12, 2011 at 1:56

Devin Burke

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answered Mar 29, 2011 at 18:26

RohitW

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