Best way to split up an array in java to smaller arrays?

Question

What is the best way to split up an array in a java method to smaller arrays? I want to be able to throw in any size array into takeReceipts(String[])

//Can handle any size array  
public void takeReceipts(String[] receipts){
//split array into smaller arrays, and then call handleReceipts(String[]) for every smaller array
}

//This method can only handle arrays with the size of 5 or less
private void handleReceipts(String[] receipts){
myNetworkRequest(receipts);
}

EDIT:

So it seems like copying the array into another array isn't efficient. Would something like this work?

    public void takeReceipts(String[] receipts){

    int limit = 5;
    int numOfSmallerArrays = (receipts.length/limit)+(receipts.length%limit);
    int from = 0;
    int to = 4;
        for (int i = 0; i < numOfSmallerArrays; i++){
            List<String> subList = Arrays.asList(receipts).subList(from, to);
            from =+ limit;
            to =+ limit;
    }

}

Your computation of numOfSmallerArrays is off - it should be int numOfSmallerArrays = ((receipts.length+limit-1)/limit); You also need to add a check if (to >= receipts.length) to = receipts.length()-1; — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Nov 18, 2014 at 18:13
My solution handles that with Math.min(i+5, receipts.length-1) — hasan
– hasan, Commented Nov 18, 2014 at 18:17
First, @dasblinkenlight why is int numOfSmallerArrays = ((receipts.length+limit-1)/limit); better than int numOfSmallerArrays = (receipts.length/limit)+(receipts.length%limit);? — EGHDK
– EGHDK, Commented Nov 18, 2014 at 18:19
Second, @dasblinkenlight where do I want to add that if statement? — EGHDK
– EGHDK, Commented Nov 18, 2014 at 18:20

Eng.Fouad · Accepted Answer · 2014-11-18 17:57:44Z

4

You can use Arrays.copyOfRange():

int from = 0;
int to = 4;
String[] subArray = Arrays.copyOfRange(receipts, from, to)

answered Nov 18, 2014 at 17:57

Eng.Fouad

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5 Comments

royhowie Over a year ago

Isn't System.arraycopy faster?

Eng.Fouad Over a year ago

Arrays.copyOfRange() uses System.arraycopy() internally.

EGHDK Over a year ago

I'm doing: Arrays.copyOfRange(receipts, from, to) from = 0 and to = 2, but the array I get back is only receipts[0] and receipts[1]. Why?

royhowie Over a year ago

@EGHDK did you read the docs he linked? "to - the final index of the range to be copied, exclusive. (This index may lie outside the array.)"

EGHDK Over a year ago

So from is inclusive and to is exclusive?

Sergey Kalinichenko · Accepted Answer · 2014-11-18 19:24:11Z

2

If you are open to using List<String> in place of String[] arrays, you could do partitioning in a very economical way:

List<String> subList = Arrays.asList(receipts).subList(from, to);

This approach does not make a copy of your array, providing a read-only view into the original array of receipts.

static final int LIMIT = 10;

public static void process(List<String> small) {
    if (small.size() > LIMIT) {
        System.out.print("Array is too big: "+small.size());
        return;
    }
    for (String s : small) {
        System.out.print(s+" ");
    }
    System.out.println();
}

public static void processBig(String[] receipts) {
    int numChunks = ((receipts.length+LIMIT-1)/LIMIT);
    int from = 0;
    int to = LIMIT;
    List<String> bigList = Arrays.asList(receipts);
    for (int i = 0 ; i != numChunks ; i++) {
        List<String> subList = bigList.subList(from, to);
        process(subList);
        from += LIMIT;
        to += LIMIT;
        if (to >= receipts.length) {
            to = receipts.length;
        }
    }
}

Demo.

The consequences of taking this approach are that the changes made to the original array elements become "visible" through the view, and that you cannot change the resultant subList in any way.

edited Nov 18, 2014 at 19:24

answered Nov 18, 2014 at 18:02

Sergey Kalinichenko

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1 Comment

EGHDK Over a year ago

How would I implement this in the takeReceipts(String[] receipts) method? Check my update. Thanks

hasan · Accepted Answer · 2014-11-18 20:07:47Z

1

public void takeReceipts(String[] receipts){
    for (int i=0; i< receipts.length; i+=5)
        handleReceipts(Arrays.copyOfRange(receipts, i, Math.min(i+4, receipts.length-1)));
}

private void handleReceipts(String[] receipts){ 
}

OR

public void takeReceipts(String[] receipts){
    for (int i=0; i< receipts.length; i+=5)
        handleReceipts(Arrays.asList(receipts).subList(i, Math.min(i+4, receipts.length-1)));
}

private void handleReceipts(List<String> receipts){
}

edited Nov 18, 2014 at 20:07

answered Nov 18, 2014 at 18:03

hasan

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