안녕하세요 강의 잘 듣고 있습니다.  마라톤 데이터 가공 2 강의를 듣던 중 Step 5단계에서 오류가 발생합니다. 사용하고 있는 파이썬 버전은 3.8.12이고 pandas 버전은 1.3.4입니다.    강의 내용대로 순차적으로 실습 진행 중 Step 5단계에서 오류가 발생하여 Step 5단계의 다른 내용을 모두 주석 후에    marathon_2015_2017['5K'] = pd.to_timedelta(marathon_2015_2017['5K'])   이 코드만 실행해 보았는데요 그럼에도 오류가 발생합니다. 혹시나 해서 csv파일을 열어 보았는데 시간데이터 중 '-' 로 표시된 부분이 종종 있었습니다. 제 생각에는 '-'라는 문자가 있으니 null도 아니고 시간데이터도 아니다 보니 문제가 발생하는 것 같은 예감입니다.    아래에 오류 내용을 그대로 첨부하겠습니다.  도움 주시면 감사하겠습니다. --------------------------------------------------------------------------- ValueError Traceback (most recent call last) /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.array_to_timedelta64() /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.parse_timedelta_string() ValueError: symbols w/o a number During handling of the above exception, another exception occurred: ValueError Traceback (most recent call last) /var/folders/zl/7hy5k6z55zz2b286tv4bbk740000gn/T/ipykernel_48790/1493613945.py in <module> 6 7 # Convert using pandas to_timedelta method ----> 8 marathon_2015_2017['5K'] = pd.to_timedelta(marathon_2015_2017['5K']) 9 # marathon_2015_2017['10K'] = pd.to_timedelta(marathon_2015_2017['10K']) 10 # marathon_2015_2017['15K'] = pd.to_timedelta(marathon_2015_2017['15K']) /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/core/tools/timedeltas.py in to_timedelta(arg, unit, errors) 122 return arg 123 elif isinstance(arg, ABCSeries): --> 124 values = _convert_listlike(arg._values, unit=unit, errors=errors) 125 return arg._constructor(values, index=arg.index, name=arg.name) 126 elif isinstance(arg, ABCIndex): /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/core/tools/timedeltas.py in _convert_listlike(arg, unit, errors, name) 171 172 try: --> 173 td64arr = sequence_to_td64ns(arg, unit=unit, errors=errors, copy=False)[0] 174 except ValueError: 175 if errors == "ignore": /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/core/arrays/timedeltas.py in sequence_to_td64ns(data, copy, unit, errors) 989 if is_object_dtype(data.dtype) or is_string_dtype(data.dtype): 990 # no need to make a copy, need to convert if string-dtyped --> 991 data = objects_to_td64ns(data, unit=unit, errors=errors) 992 copy = False 993 /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/core/arrays/timedeltas.py in objects_to_td64ns(data, unit, errors) 1098 values = np.array(data, dtype=np.object_, copy=False) 1099 -> 1100 result = array_to_timedelta64(values, unit=unit, errors=errors) 1101 return result.view("timedelta64[ns]") 1102 /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.array_to_timedelta64() /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.array_to_timedelta64() /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.convert_to_timedelta64() /opt/homebrew/Caskroom/miniforge/base/envs/DV/lib/python3.8/site-packages/pandas/_libs/tslibs/timedeltas.pyx in pandas._libs.tslibs.timedeltas.parse_timedelta_string() ValueError: symbols w/o a number