How to find the minimum value in an ArrayList, along with the index number? (Java)

You can use Collections.min and List.indexOf:

int minIndex = list.indexOf(Collections.min(list));

If you want to traverse the list only once (the above may traverse it twice):

public static <T extends Comparable<T>> int findMinIndex(final List<T> xs) {
    int minIndex;
    if (xs.isEmpty()) {
        minIndex = -1;
    } else {
        final ListIterator<T> itr = xs.listIterator();
        T min = itr.next(); // first element as the current minimum
        minIndex = itr.previousIndex();
        while (itr.hasNext()) {
            final T curr = itr.next();
            if (curr.compareTo(min) < 0) {
                min = curr;
                minIndex = itr.previousIndex();
            }
        }
    }
    return minIndex;
}

This should do it using built in functions.

public static int minIndex (ArrayList<Float> list) {
  return list.indexOf (Collections.min(list)); }

try this:

public int getIndexOfMin(List<Float> data) {
    float min = Float.MAX_VALUE;
    int index = -1;
    for (int i = 0; i < data.size(); i++) {
        Float f = data.get(i);
        if (Float.compare(f.floatValue(), min) < 0) {
            min = f.floatValue();
            index = i;
        }
    }
    return index;
}