In R you can do something like this:
> x = c(1, 222, 333, 4, 5)
> x[c(2, 3)]
[1] 222 333
> in the beginning of line is just a prompt in an interactive session. x is a vector of numeric values, and if you want the 2nd and 3rd element of x, you pass another vector c(2, 3) to index x. This is different from Arrays.copyOfRange in java: you can pass an arbitrary index vector to x, not necessarily in a continuous range, i.e. x[c(1,3,5)]
I am wondering if there is a similar feature in java.
As I understood your question, you could create a method that take a list of indexes as parameters.
For generic arrays, you'll need to use Array.newInstance and cast the resulting array to T[] (thanks and kudos for @Radiodef for pointing this out)
//for lists
static <T> List<T> buildList(List<T> original, int... indexes){
List<T> finalList = new ArrayList<>();
for(int index : indexes){
finalList.add(original.get(index));
}
return finalList;
}
//for arrays
static <T> T[] buildArray (T[] original, int... indexes){
@SuppressWarnings("unchecked")
T[] finalArray = (T[])Array.newInstance(original.getClass().getComponentType(), indexes.length);
for(int i = 0; i < indexes.length; i++){
finalArray[i] = original[indexes[i]];
}
return finalArray;
}
Few notes :
int[] or double[]), you'll have to overload the methods, that's why I suggest you to use a List with generics instead. LinkedList instead of an ArrayList, be aware that #get(int index) is an O(n) operation instead of O(1)Example of usage :
public static void main(String[] args) {
Integer[] xArray = {-1, 10, 24, 7};
List<Integer> xList = Arrays.asList(-1, 10, 24, 7);
System.out.println(Arrays.toString(buildArray(xArray, 0, 2)));
System.out.println(buildList(xList, 0, 1, 3));
}
Which outputs:
[-1, 24]
[-1, 10, 7]
buildArray for T[] is incorrect. You need to use Arrays.copyOf or Array.newInstance. You can't do (T[])new Object[n] in a context where the array is returned. It will throw an exception.
Object[] to T[]!! Try this: String[] arr = buildArray(new String[]{"a", "b"}, 0, 1);Array#newInstance as in (T[])Array.newInstance(original.getClass().getComponentType(), indexes.length). Your answer is otherwise good.take a look at Arrays.copyOfRange
Rhave indices from1or from0? The arrays in Java start indices from0.