def shortest_row_F(F1):
    """
    Get the minimum and maximum length of the elements of F1.
    
    Parameters
    ----------
     F1 : list of numpy 1D arrays.
     
    Returns
    -------
     shortest_row
         length of the shortest element in F1.
     longest_row
         length of the longest element in F1.
    """
    shortest_row=-1
    longest_row=-1
    for i in range(len(F1)):
        if (shortest_row<0)or(len(F1[i])<shortest_row):
            shortest_row=len(F1[i])
        if (shortest_row<0)or(len(F1[i])>longest_row):
            longest_row=len(F1[i])
    return([shortest_row,longest_row])