Choose random String from two dimensional array?

Question

So what I have is a 2d array with the name of the drink, and the price Test[Name][Price]:

    public static final String[][] Test = {{"vodka1","5.0"},{"vodka2","10.0"},{"vodka3","15.0"},{"vodka4","20.0"},{"vodka5","25.0"}};

What im trying to do is have it so that the user inputs their max price and then a drink is randomly chosen from the 2d array that is below their max price.

So first of all how do i narrow down the array to just the drinks that are lower than the users max price?

This is what i tried ( I know its wrong but its all i could think of):

    private static final String[] test1 = {};
    test1 = (array_city.Test[i][j] <= Price);
                    randomIndex = random.nextInt(test1.length);
                    text2.setText(test1[randomIndex]);

Thanks!

EDIT

I have sorted my array into least to greatest according to prices and tried this code in order to find the greatest drink possible to buy, pick a random index somehwere between , and then setText to that string but when the activity page starts it crashes? Here is my code:

    convert = Double.valueOf(array_city.Test[c][1]);
                    // Set vodka brand
                    while(Price <= convert){
                        c++;
                        convert = Double.valueOf(array_city.Test[c][1]);
                    }
                    final TextView text2 = (TextView) findViewById(R.id.display2);
                    randomIndex = random.nextInt(c);
                    text2.setText(array_city.Test[randomIndex][1]);

Why does this not work?

FINAL EDIT

Figured it out!! turned out to be some minor logic issues, changed to a four loop and it works great!! here is what i did to my code:

    convert = Double.valueOf(array_city.Test[c][1]);
                    // Set vodka brand
                    for(double i = Price; i >= convert;){
                        c++;
                        convert = Double.valueOf(array_city.Test[c][1]);
                    }
                    final TextView text2 = (TextView) findViewById(R.id.display2);
                    randomIndex = random.nextInt(c);

he's asking if the prices will always be in order in the array from smallest to largest [1,2,3,4,5] etc.. and not [3,5,2,1,4].. if the array is always sorted, then you can just ignore the portion above/below the value. — Austin Greco
– Austin Greco, Commented Sep 4, 2012 at 20:43
Okay. I'm just asking if the array is always sorted by price. Because if it is, then you can calculate the index of the drink with the maximum price that you can still buy, and generate a random number between 0 and that index (inclusive) and output the drink at that index. — eboix
– eboix, Commented Sep 4, 2012 at 20:44
@eboix alright and no it is not, the array could be in any order [3,87,2,65] (just an example) — Mr. Pivirotto
– Mr. Pivirotto, Commented Sep 4, 2012 at 20:45

eboix · Accepted Answer · 2012-09-04 21:02:39Z

2

First of all, instead of making it a String[][] array, you should make it a Drink[] array (where Drink is a class that you have defined and which has a String name, and a float price. This will help you use the info, because you won't have to constantly worry about parsing the price String to a double.

Here is a pseudocode solution if the array is sorted by price (from lowest to highest):

First find the most expensive drink that you can still buy. You could binary search for it, but a simpler solution would be to go from index 0 to Test.length-1 checking whether or not the drink would be buyable. If not, you would stop and store the index of the last buyable drink. If it were buyable, you would continue.
Then, you would generate a random int from 0 to the maxIndex (inclusive), and output the Drink.

For example,

(int)(Math.random()*(maxIndex+1)) would get you the random integer.

EDIT

Since the array is not necessarily sorted, you can sort it. In order to do this, use java.util.Arrays.sort(Object[] o, Comparator c) to sort it.

Input your Drink[] as the first parameter. And your DrinkComparator as your second. This will quicksort it for you.

Assuming that your Drink class is defined as follows:

public class Drink {

        String name;
        double price; // You could also use floats

        public Drink(String n, double p) {

            price = p;
            name = n;
        }
    }

You can make your DrinkComparator class like this.

http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Comparator.html

    class DrinkComparator implements Comparator {

         public int compare(Object o1, Object o2) {
             if(o1.price < o2.price) {
                 return 1;
             }
             else if(o1.price == o2.price) { // Disregarding float imprecision
                 return 0;
             }
             else { // Not necessary, but here for the sake of readability.
                 return -1;
             }
         }

         public boolean equals(Object o) { // I don't think you will be using this method.
             return true; // If you run into problems, tell me.
         }
    }
}

Then you would sort like this:

Arrays.sort(drinks, new DrinkComparator());

drinks would be your Drink[] of course.

edited Sep 4, 2012 at 21:02

answered Sep 4, 2012 at 20:51

eboix

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3 Comments

Mr. Pivirotto Over a year ago

look at my edit to my main post, I have tried what you suggested but its crashing now?

eboix Over a year ago

@Hockeyman271 Does it give an error message when it crashes? Can you give me all of your code?

Mr. Pivirotto Over a year ago

i worked through it and it works perfectly now!! thanks again!

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