df = pd.DataFrame({"name": ["A001", "A002", "B001", "A001_K", "C002", "B001_K", "B001"],
"protein": [25, 28, 45, 22, 60, 40, 27],
"Qty": [85, 90, 75, 80, 30, 50, 30],
"rank": ["1st", "1st", "1st", "2nd", "1st", "1st", "2nd"]})
请问我先选列表name里面的第一个元素要怎么写,谢谢