Question

使用

List<String> notizen = new ArrayList<String>();

SQLiteDatabase connection;
connection = openOrCreateDatabase(
        dbPath
        , SQLiteDatabase.CREATE_IF_NECESSARY
        , null
);

Cursor cursor = connection.rawQuery("SELECT [subject],[note],[priority] FROM tasks WHERE [c] = 'test'",null);
try {
    if (cursor.moveToFirst()) {
        do {
            if (cursor.getString(1).toString().length() > 10)
                notizen.add(cursor.getString(0).toString() + "#" + cursor.getString(1).toString() + "#" + cursor.getString(2).toString());
            else
                notizen.add(cursor.getString(0).toString() + "#" + cursor.getString(2).toString());
        } while (cursor.moveToNext());
    }
}
catch(Exception dd)
{
    int duration = Toast.LENGTH_LONG;
    Context context = getApplicationContext();
    CharSequence text = "Erra: "+dd.getMessage();
    Toast toast = Toast.makeText(getApplicationContext(), text, duration);
    toast.show();
}
connection.close();

我将subject and note and priority或subject and priority插入到字符串列表中。

我想从此列表中选择一个随机条目，但应该有一个加权函数。根据优先级，元素应更频繁地出现。 1等于最频繁，5等于最不频繁（通常是一次）。

应该有一个临时列表，例如：

subject1#note1#priority1   
subject2#note2#priority2
subject5#note5#priority5
subject1#note1#priority1  
subject2#note2#priority2
subject2#note2#priority2
subject1#note1#priority1 
subject1#note1#priority1
subject1#note1#priority1
subject2#note2#priority2

请注意，条目是随机混合的，subject1出现5次，而subject5出现一次。

我该怎么做？

Answer 1

试试这个：

class Element{
   int priority;
   String data;
}

ArrayList<Element> elements = createCoreElements();
ArrayList<Element> randomItems = new ArrayList<Element>();
for(Element element : elements){
   randomItems.add(element); // in case you want to add minimum amount of elements from each type
   for(int i = 0; i < element.priority; i++){
       if(Math.random() < 0.5){// random boolean
           randomItems.add(element);
       }
   }
}

Collections.shuffle(randomItems);
print(randomItems);

Answer 2

我自己解决了这个问题：

try {
        if (cursor.moveToFirst()) {
            do {
                if (cursor.getString(1).length() > 10) {
                    if (cursor.getString(2).equals("5")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("4")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("3")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("2")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("1")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(1) + "#" + cursor.getString(2));
                    }
                }
                else {
                    if (cursor.getString(2).equals("1")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("2")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("3")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("4")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                    }
                    if (cursor.getString(2).equals("5")) {
                        notizen.add(cursor.getString(0) + "#" + cursor.getString(2));
                    }
                }
            } while (cursor.moveToNext());
        }
    }
    catch(Exception dd)
    {
        //
    }
    connection.close();

从字符串数组中随机选择元素但使用权重

2 个答案: