java:如何将2d数组分割成两个2d数组

I'm writing a program to multiply matrices (2d arrays) as efficiently as possible, and for this i need to split my two arrays into two each and send them off to a second program to be multiplied. The issue I have is how to split a 2d array into two 2d arrays, at specific points (halfway). Does anyone have any ideas?

我正在编写一个程序来尽可能高效地相乘矩阵(2d数组)，为此，我需要将两个数组分别分割成两个数组，并将它们发送给第二个要相乘的程序。我的问题是如何在特定的点(中间)将一个2d数组分割成两个2d数组。有人有什么想法吗?

1 个解决方案

#1

Lets say you have a 2d array of strings like so

假设你有一个二维的字符串数组


String[][] array= new String[][]
{
    {"a","b","c"},
    {"d","e","f"},
    {"h","i","j"},
    {"k","l","m"}
};

Now you need a way to split these arrays at the half way point. Lets get the halfway point. Figure out how big the array is and then cut it in half. Note that you also must handle if the array is not an even length. Example, length of 3. If this is the case, we will use the Math.floor() function.

现在，您需要一种方法来将这些数组分割到中间点。让我们得到中点。算出数组的大小，然后把它切成两半。注意，如果数组不是偶数，也必须处理。例子中,长度3。如果是这种情况，我们将使用Math.floor()函数。


int arrayLength = array.length;
int halfWayPoint = Math.floor(arrayLength/2);
//we also need to know howmany elements are in the array
int numberOfElementsInArray = array[0].length;

Now we have all the info we need to create two 2d arrays from one. Now we must explicitly copy create and copy the data over.

现在我们已经有了创建两个二维数组所需的所有信息。现在，我们必须显式地复制创建和复制数据。


//the length of the first array will be the half way point which we already have
String [][] newArrayA = new String[halfWayPoint][numberOfElementsInArray];
//this copies the data over
for(int i = 0; i < halfWayPoint; i++)
{
    newArrayA[i] = array[i];
}

//now create the other array
int newArrayBLength = array.length - halfWayPoint;
String[][] newArrayB = new String[newArrayBLength][numberOfElementsInArray];
/*
 * This copies the data over. Notice that the for loop starts a halfWayPoint.
 * This is because this is where we left of copying in the first array.
 */
for(int i = halfWayPoint; i < array.length; i++)
{
    newArrayB[i] = array[i];
}

And your done!

和你做的!

Now if you want to do it a little nicer, you could do it like this

如果你想做得更好，你可以这样做


int half = Math.floor(array/2);
int numberOfElementsInArray = array[0].length;
String [][] A = new String[half][numberOfElementsInArray];
String [][] B = new String[array.length - half][numberOfElementsInArray];
for(int i = 0; i < array.length; i++)
{
    if(i < half)
    {
        A[i] = array[i];
    }
    else
    {
        B[i] = array[i];
    }

}

And lastly, if you dont want to do it explicitly, you can use the built in functions. System.arraycopy() is one example. Here is a link to its api System.arraycopy()

最后，如果你不想显式地做，你可以使用内置函数。System.arraycopy()就是一个例子。下面是它的api System.arraycopy()的链接


int half = Math.floor(array/2);
int numberOfElementsInArray = array[0].length;
String [][] A = new String[half][numberOfElementsInArray];
String [][] B = new String[array.length - half][numberOfElementsInArray];
System.arraycopy(array,0,A,0,half);
System.arraycopy(array,half,B,0,array.length - half);

#1