def decimate(it, nd=10):
    """
    Return first then each 'nd' elements from iterable 'it'.

    Parameters
    -----------

    it : iterable
        Input data.

    nd : int
        Decimation factor

    Returns
    -------

    l : list
        One in 'nd' values from 'it'.

    """
    assert isinstance(nd, int), "'nd' is not an integer: {0!r}".format(nd)
    assert nd > 0, "'nd' is not a positive integer: {0!r}".format(nd)
    l = list()
    n = 0
    for el in it:
        if not n % nd:
            l.append(el)
        n += 1
    return l
