java linkedhashmap iteration

Question

I have two hashmap

LinkedHashMap<String, int[]> val1 = new LinkedHashMap<String, int[]>();
LinkedHashMap<String, int> val2 = new LinkedHashMap<String, int>();

each hashmap has different key and values. I am trying to iterate over both hashmap at the same time and multiply each value of val1->int[] to val2->int

What is the easiest and fasted way to do it? I have thousands values in both hashmap.

Thanks

Hmm, if they have different keys, then what does it mean to iterate over them at the same time? Say val1 has keys "a" and "b", while val2 has keys "X" and "Y". Does that mean you want to handle all four combinations (aX, aY, bX, bY), or what? — Vance Maverick
– Vance Maverick, Commented Mar 27, 2011 at 4:22
Example versions of val1 and val2 with expected output will go a long way. — Andrew White
– Andrew White, Commented Mar 27, 2011 at 4:24
A LinkedHashMap has a iteration ordering, so, if he iterates from front to end, there's only one way he/she can do it. — Dhaivat Pandya
– Dhaivat Pandya, Commented Mar 27, 2011 at 4:29
logically val1 and val2 have relationship. val1->int[] contains multiple months' expense and val2->int contains the number of people. Now I want to iterate to multiple each month expense with number of people to get some values for further processing. val1 and val2 will always have same size — Tweet
– Tweet, Commented Mar 27, 2011 at 4:35

KarlP · Accepted Answer · 2011-03-28 10:23:32Z

1

You are probably doing it wrong...

First, a HashMap can't store ints, it needs proper objects - like Integer – An array is an object, although it's hidden behind some syntactic sugar.

Here's how to loop over both maps, if they happens to have the same size, which is what I think you mean.

    Iterator<int[]> expenses = val1.values().iterator();
    Iterator<Integer> people = val2.values().iterator();

    assert val1.size() == val2.size() : " size mismatch";
    while (expenses.hasNext()) {
        int[] expensesPerMonth = expenses.next();
        int persons = people.next();

        // do strange calculation
        int strangeSum = 0;
        for (int idx = 0; idx < expensesPerMonth.length; idx++) {
            strangeSum += persons * expensesPerMonth[idx];
        }
        System.out.println("strange sum :" + strangeSum);
    }

But You should probably go back and rethink how you store your data – why are you using maps, and whats the key?

Wouldn't it be better to create an object that represents the combination of monthly expenses and number of people, for instance?

edited Mar 28, 2011 at 10:23

answered Mar 27, 2011 at 9:07

KarlP

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1 Comment

Tweet Over a year ago

Thanks, I know it is wrong logic but I am not main developer. I am just maintaining.

Dhaivat Pandya · Accepted Answer · 2011-03-27 04:35:17Z

0

AFAIK, a LinkedHashMap has iteration ordering. So, something like this may work:

Iterator myIt1 = val1.entrySet().iterator();
Iterator myIt2 = val2.entrySet().iterator();

while(val1.hasNext() && val2.hasNext()) {
    int myarray[] = val1.next();
    for(int i = 0; i<myarray.length; i++) {
        myarray[i] = myarray[i] * val2.next();
    }
}

answered Mar 27, 2011 at 4:35

Dhaivat Pandya

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3 Comments

Tweet Over a year ago

for using val2.next(), it gives an error that The method next() is undefined for the type LinkedHashMap<String,int[]>

I82Much Over a year ago

You're advancing iterator2 too often. (At least according to my interpretation of the question)

Tweet Over a year ago

Could you please check your code again? it has several errors :(

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