can I copy an array to a hash table?

I hav开发者_Python百科e an array which its elements are float .how can I copy this array to a hash table?

thanks

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You can easily put them into a Hashtable of int -> float. The following method will use their index in the array as the key.

float[] arr;
Hashtable<Integer, Float> table = new Hashtable<Integer, Float>(arr.length);
for (int i = 0; i < arr.length; i++) {
    table.put(i, arr[i]);
}

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An array cannot directly correspond to a Map. It can correspond to a set.

new HashSet(Arrays.asList(array))

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Hashtable implements Map, so you would need to pair every float with some key.

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Given the OP's clarification of his/her requirements in jjnguy's answer, here's an O(n) (amortized) way to count occurrences of unique values in a float array:

float[] values;
Map<Float, Integer> occurrences = new HashMap<Float, Integer>();
for ( float f : values ) {
    int count = occurrences.containsKey(f) ? occurrences.get(f) : 0;
    occurrences.put(f, count+1);
}

//then find multiple occurrences by finding entries with a value > 0
for ( Entry<Float, Integer> entry : occurrences.values() ) {
    if ( entry.getValue() > 1 ) {
       System.out.println("Duplicate: " + entry.getKey());
    }
}

In practice it's usually smelly to use a float as a key to anything, or to use a float in a way that pretends it's a discrete value. Floating point types are typically used to simulate "continuous" values, where for all intents and purposes 7.000000000012 should be considered the same as 7.000000000013.

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If you want to know how many there are of different float values in your array, the best solution would be a multiset (which is typically built on top of a Map<T, Integer>). With Guava, you could do this:

float[] floats = ...
Multiset<Float> multiset = HashMultiset.create(Floats.asList(floats));
for (Multiset.Entry<Float> entry : multiset.entrySet()) {
  Float value = entry.getElement();
  int count = entry.getCount();
  ...
}