Compare and sort java 2Darray using an element from the subarray-CodePudding

void sortPrice () throws IOException {
            //create a bufferedReader and user scanner
            BufferedReader br = new BufferedReader(new FileReader("items.txt"));
            Scanner sc = new Scanner(System.in);
            List lines = new ArrayList();
            //create a 2D arrayList and append each line of the txt file into a sub-array in the 2D array
            for(String line = br.readLine(); line != null; line = br.readLine()){
                String[] currentLine = line.split(",");
                lines.add(currentLine);
            }
String[][] strings = (String[][]) lines.toArray(new String[lines.size()][]);

I have this code that read from items.txt file and turn it into 2d array

I001-2001, Dell XPS 17,5.5, Laptop

I002-1988, Macbook Pro 15, 8.5, Laptop

I003-1992, Samsung Galaxy S22, 4.5, Phone I004-1999, Iphone 13 PM, 7.5, Phone

I005-2015, Harman Kardon, 3.5, Earbud

This is what inside the file TXT. I want to sort the item by the third element inside this sub-array which is the price for the item, but since I created the array as the String, it cannot be sort with interger value, I'm new to java so sorry for any techinicality.

CodePudding user response：

There is a helper function Arrays.sort (Docs).

It takes two arguments, an array of things (technically objects, in practice, anything including other arrays), and a custom comparator as a second parameter.

Therefore, you can create a custom comparator like this:

public class MyProductComparator implements Comparator<String[]> {
 
    @Override
    public int compare(String[] prod1, String[] prod2) {
        // Compare the element at index 2 of both arrays
        return prod1[2].compareTo(prod2[2]);
    }
}

Afterward, you can use it like this:

Arrays.sort(strings, new MyProductComparator());

Additionally, java already provides some standard comparator implementations, for example, one that takes two elements and compares them based on a predefined key. This is quite useful and simplifies your code greatly.

// compare using  the second element
Arrays.sort(strings, Comparator.comparing(o -> o[2]))

CodePudding user response：

Files.lines will read in the file and put each line in a stream for processing. The lines can then be sorted before collecting into a list.

map the lines to an Abstract.SimpleEntry to hold the actual line as the key and the double as the value on which to sort.
The value is split on comma, trimmed of whitespace and retrieved as item 2. Then converted to a Double.
then sort the stream using the entry's value.

void sortPrice () throws IOException {
   list = Files.lines(Path.of("f:/items.txt"))
        .map(item -> new SimpleEntry<String, Double>(item,
                Double.parseDouble(
                        item.split(",")[2].trim())))
        .sorted(Entry.comparingByValue()).map(Entry::getKey)
        .toList();
}

list.forEach(System.out::println);

prints

I005-2015, Harman Kardon, 3.5, Earbud
I003-1992, Samsung Galaxy S22, 4.5
001-2001, Dell XPS 17,5.5, Laptop
Phone I004-1999, Iphone 13 PM, 7.5, Phone
I002-1988, Macbook Pro 15, 8.5, Laptop

Note: if you are going to make use of these fields, it would be best to create a class to hold them in their final converted types.