How can I convert a Set<Set<String>> to a String[][]? I have tried .toArray(new String[0]) but this doesn't seem to do the trick.
Thanks! Christian
Add a comment
|
3 Answers
For each Set<String> s in the outer set, convert s to String[] and add it to your Array of arrays.
I don't know any built in way to create n-dimensional arrays from nested collections.
4 Comments
Christian Stewart
Isn't this painfully slow?
Philipp
What do you think the implementation of Set.toArray() does internally? The JVM isn't magic.
AlexWien
@ChristianStewart why slow? it makes no difference if you loop or if java does it internally.
atamanroman
Well it isn't the perfect solution. If it's a bottleneck I'd go and stick with arrays. If it's not don't convert since arrays behave vastly different than sets. You would lose all the guarantees set gives you.
Loop through the set and create the array
Comments
Try below code, it works
package com.rais;
import java.util.HashSet;
import java.util.Set;
/**
* @author Rais.Alam
* @date Dec 17, 2012
*/
public class SetClient
{
/**
* @param args
*/
public static void main(String[] args)
{
Set<Set<String>> myArray = new HashSet<Set<String>>();
Set<String> arr1 = new HashSet<String>();
Set<String> arr2 = new HashSet<String>();
Set<String> arr3 = new HashSet<String>();
arr1.add("a-1");
arr1.add("a-2");
arr1.add("a-3");
arr2.add("b-1");
arr2.add("b-2");
arr2.add("b-3");
arr3.add("c-1");
arr3.add("c-2");
arr3.add("c-3");
arr3.add("c-4");
arr3.add("c-5");
myArray.add(arr1);
myArray.add(arr2);
myArray.add(arr3);
String[][] outputArray = convertSetOfSetToArray(myArray);
for (String[] outerArr : outputArray)
{
for (String value : outerArr)
{
if (value != null)
{
System.out.println(value);
}
}
}
}
public static String[][] convertSetOfSetToArray(Set<Set<String>> myArray)
{
int secondArraySize = 0;
/*
* Looping array to get the size.
*/
for (Set<String> innerSet : myArray)
{
if (innerSet.size() > secondArraySize)
{
secondArraySize = innerSet.size();
}
}
// Declaring and initializing String arrays;
String[][] outputArray = new String[myArray.size()][secondArraySize];
int firstIndex = 0;
int secondIndex = 0;
for (Set<String> innerSet : myArray)
{
for (String value : innerSet)
{
outputArray[firstIndex][secondIndex] = value;
secondIndex++;
}
secondIndex = 0;
firstIndex++;
}
return outputArray;
}
}
