java - convert primitive double array to collection

Question

I'm looking to have an array of floats(doubles) & integers as below -

double[] myArr = {0, 0, 95, 9.5, 19, 610.5, 1217, 5.14, 4038.66, 10.23, 7961, 828, 199858, 37325.3};

I then have this function that returns the max & min

    public static void getMaxArrVal(double[] myArr) {           

        myCol = /* Code to convert myarr to collection should come here */
        System.out.println(Collections.min(myCol ));
        System.out.println(Collections.max(myCol ));
    }
}

getMaxArrVal(myArr);

I'm having problems converting primitive data type to a collection.I tried converting this to double list, tried by converting myArr to char/String to check a few things but nothing has worked obviously.

I keep seeing the compilation error of primitive data type. I did try Double too but no luck.

How could I possibly convert the array to collection & calculate min/max on this one. I'd appreciate any help her please.

@prasad is correct; this question is essentially an exact duplicate. — bcsb1001
– bcsb1001, Commented Mar 6, 2016 at 9:29

Community · Accepted Answer · 2017-05-23 12:03:05Z

4

This works nicely with Java 8:

Arrays.stream(myArr).boxed().collect(Collectors.toCollection(ArrayList::new));

Any Collection may be used instead of ArrayList, of course. The code I have here may actually be simplified to Collectors.toList().

Also, as noted in @nukie's answer, DoubleStream has its own min() and max() methods, rendering the conversion useless. Merely use two streams created using Arrays.stream(myArr) and call these methods.

edited May 23, 2017 at 12:03

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answered Mar 6, 2016 at 9:20

bcsb1001

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Comments

luk · Accepted Answer · 2016-03-06 09:18:02Z

2

Guava comes with nice solution

Lists.newArrayList(double[])

answered Mar 6, 2016 at 9:18

luk

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Comments

Atuos · Accepted Answer · 2016-03-06 09:21:10Z

1

double[] primitives = new double[] { 1.0, 2.0, 3.0};
List<Double> objects = new ArrayList<>();
for(double num : primitives) {
    objects.add(num);
}

answered Mar 6, 2016 at 9:21

Atuos

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Comments

mikefaheysd · Accepted Answer · 2016-03-06 09:26:04Z

1

Using Arrays.sort will sort your array in ascending order. Therefore, you know the min will be the first element of your array, myArr[0], and your max will be the last element in your array myArr[myArr.length-1].

double[] myArr = {0, 0, 95, 9.5, 19, 610.5, 1217, 5.14, 4038.66, 10.23, 7961,  828, 199858, 37325.3};
Arrays.sort(myArr);
System.out.println(myArr[0]);
System.out.println(myArr[myArr.length-1]);

The following will result in

0.0 <-- min

199858.0 <-- max

answered Mar 6, 2016 at 9:26

mikefaheysd

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2 Comments

Ken Bekov Over a year ago

This approach will change original array's order. But if OP don't cares - perfect solution.

usert4jju7 Over a year ago

Thank you Mike. I need the array order to remain the same.

nukie · Accepted Answer · 2016-03-06 09:27:39Z

1

if you run this code at java8 you can try lambdas:

Arrays.stream(myArr).max();

and

Arrays.stream(myArr).max();

edited Mar 6, 2016 at 9:27

answered Mar 6, 2016 at 9:18

nukie

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3 Comments

bcsb1001 Over a year ago

Please check your spelling, and also your code. This won't work because primitive streams like the generated DoubleStream don't accept Collectors in their collect() method. Stream is not spelt straem.

nukie Over a year ago

thank you for remark! this was unexpected for me that DoubleStream not provide collect(Collector) method )

bcsb1001 Over a year ago

It wouldn't make much sense, as Collectors are generic and you can't have a Collector<double, X, X>. Still, we all wish things like this could be possible sometimes.

Yassin Hajaj · Accepted Answer · 2016-03-06 10:06:24Z

1

public static void main(String[] args) throws Exception {

    Double [] myArr = {0., 0., 95., 9.5, 19., 610.5, 1217., 5.14, 4038.66, 10.23,  7961., 828., 199858., 37325.3};      

    Double min = Arrays.stream(myArr).min(Comparator.<Double>naturalOrder()).get();
    Double max = Arrays.stream(myArr).max(Comparator.<Double>naturalOrder()).get();

    System.out.println(min);
    System.out.println(max);
}

If you don't need collection to anything else, except find max and min, create stream right from array. In this case you don't need create separate collection at all.

edited Mar 6, 2016 at 10:06

Yassin Hajaj

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answered Mar 6, 2016 at 9:22

Ken Bekov

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3 Comments

Yassin Hajaj Over a year ago

Do not forget a Stream object can only be used once. Just use Arrays.stream(myArr) twice...

Ken Bekov Over a year ago

@YassinHajaj I did. And you're right. Thanx for comment.

usert4jju7 Over a year ago

Thank you Ken. I prefer double as I've written quite a lot of code with that type. So Double doesn't quite work in this situation. However, this is a good future reference for me. Thank you

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