How to convert String Array to Double Array in one line

Question

I have a string array as:

String[] guaranteedOutput = Arrays.copyOf(values, values.length,
String[].class);

All the String values are numbers. The data should be converted to a Double[].

Question
Is there a one line solution in Java to achieve this or we need to loop and convert each value to a Double?

Why not double[]? It's faster.

Has QUIT--Anony-Mousse
– Has QUIT--Anony-Mousse

2012-02-01 18:40:00 +00:00
Commented Feb 1, 2012 at 18:40 — Has QUIT--Anony-Mousse
– Has QUIT--Anony-Mousse, Commented Feb 1, 2012 at 18:40
Loop and convert each one of them, is what you can do.

asgs
– asgs

2012-02-01 18:40:23 +00:00
Commented Feb 1, 2012 at 18:40 — asgs
– asgs, Commented Feb 1, 2012 at 18:40

Michael Berdyshev · Accepted Answer · 2020-03-21 15:32:22Z

39

Java 8 Stream API allows to do this:

double[] doubleValues = Arrays.stream(guaranteedOutput)
                        .mapToDouble(Double::parseDouble)
                        .toArray();

Double colon is used as a method reference. Read more here.

Before using the code don't forget to import java.util.Arrays;

UPD: If you want to cast your array to Double[], not double[], you can use the following code:

Double[] doubleValues = Arrays.stream(guaranteedOutput)
                        .map(Double::valueOf)
                        .toArray(Double[]::new);

edited Mar 21, 2020 at 15:32

answered Sep 3, 2016 at 14:06

Michael Berdyshev

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Comments

JB Nizet · Accepted Answer · 2012-02-01 18:39:06Z

13

Create a method implementing it using a loop, then call your method, and you'll have a one-line solution.

There is no buit-in method in the Java API to do that.

answered Feb 1, 2012 at 18:39

JB Nizet

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Comments

alain.janinm · Accepted Answer · 2012-02-01 18:51:51Z

6

In one line :p

Double[] d=new ArrayList<Double>() {{for (String tempLongString : tempLongStrings) add(new Double(tempLongString));}}.toArray(new Double[tempLongStrings.length]);

answered Feb 1, 2012 at 18:51

alain.janinm

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Comments

Yeabkal Wubshit · Accepted Answer · 2018-05-02 10:22:58Z

4

This will convert an array of strings to an array of doubles in one line.

String[] stringArray = {"1.3", "4.6", "3.2"};
double[] doubleArray = Arrays.stream(stringArray).mapToDouble(Double::parseDouble).toArray();

answered May 2, 2018 at 10:22

Yeabkal Wubshit

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1 Comment

speedstyle Over a year ago

this should work with map as well as mapToDouble (and might be negligibly faster?)

Has QUIT--Anony-Mousse · Accepted Answer · 2012-02-01 18:41:11Z

2

What is wrong with a loop?

double[] parsed = new double[values.length];
for (int i = 0; i<values.length; i++) parsed[i] = Double.valueOf(values[i]);

is not particularly clumsy. Plus, you can easily add proper error handling.

Of course you can easily wrap this as you like.

OpenJDK8 will probably bring lambda expressions, and using Double.valueOf as "map" function would be a prime example for using this.

answered Feb 1, 2012 at 18:41

Has QUIT--Anony-Mousse

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Comments

Adam Mihalcin · Accepted Answer · 2012-02-01 18:42:25Z

2

You want a map operation from functional programming, which unfortunately Java does not offer. Instead, you have to loop as

double[] nums = new double[guaranteedOutput.length];
for (int i = 0; i < nums.length; i++) {
    nums[i] = Double.parseDouble(guaranteedOutput[i]);
}

answered Feb 1, 2012 at 18:42

Adam Mihalcin

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Comments

Arthur Neves · Accepted Answer · 2012-02-01 18:47:28Z

1

CollectionUtils.collect(guaranteedOutput, new Transformer() { 
        public Object transform(Object i) { 
            return Double.parseDouble(i); 
        }  
});

EDIT

Keep in mind that this is no in JavaSDK ! I am using http://commons.apache.org/collections/apidocs/org/apache/commons/collections/CollectionUtils.html

edited Feb 1, 2012 at 18:47

answered Feb 1, 2012 at 18:41

Arthur Neves

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2 Comments

Brian Roach Over a year ago

You were missing a semicolon and the formatting made it difficult to read; fixed that. It's also worth noting that this is not part of core java but rather part of org.apache.commons.collections - that being said, excellent answer. (I'd +1 you but I'm out of votes for the day)

Arthur Neves Over a year ago

lol! thanks for the edit! I kind of like commons collections for this purposes!

Carlos · Accepted Answer · 2012-02-01 18:40:30Z

0

I think you're going to have to loop through and convert each value over to a double. This is how I did it in one of my other questions:

for(getData : getDataArray){
 double getTotal;
 getTotal = getTotal + Double.parseDouble(getData);
}
return getTotal;

The idea is the same. Turn that into a method, pass your paramters and you're golden.

answered Feb 1, 2012 at 18:40

Carlos

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2 Comments

Has QUIT--Anony-Mousse Over a year ago

Except that you are missing a type in your for loop; and if he wants to get an array out (as opposed to a list that he can append to), you will actually need to know the integer index.

Carlos Over a year ago

I didn't clarify that the code I provided is a snip from a Beanshell script that I worked on, hence the lack of a data type.

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