def copy_condensed(obj, index:int = 0):
    """Copies an object recursively while dropping all but one element of lists.

    Typically for objects converted from JSON data, for basic visualization of contents.

    Example usage:

    >>> import json
    >>> with open('foo.json') as f:
    ...     data_dict = json.load(f)
    ...
    >>> compact_dict = copy_condensed(data_dict, -1)
    >>> print(json.dumps(compact_dict, indent=2))
    {
      "activity": [
        "136 items",
        {
          "average_met": 1.09375,
          "cal_active": 4,
          "cal_total": 1957
        }
      ],
      "sleep": [
        "124 items",
        {
          "awake": 720,
          "deep": 7860,
          "duration": 21900,
          "efficiency": 97,
          "hr_5min": [
            "74 items",
            46
          ]
        }
      ]
    }

    :param obj: Object to be condensed
    :type obj: dict, list, int, float, str
    :param index: Index of list element to be kept
    :type index: int
    :returns Condensed object
    """
    if type(obj) is list:
        return [f"{len(obj)} items", copy_condensed(obj[index], index)]
    elif type(obj) is dict:
        return {k: copy_condensed(v, index) for k,v in obj.items()}
    else:
        assert type(obj) in [int, float, str]
        return obj