解決 ValueError: If using all scalar values, you must pass an index¶

這個錯誤通常出現在沒有設定索引時，想要建立一個 DataFrame。¶

In [2]:

import pandas as pd
dict1 = {1:"a", 2:"b", 3:"c", 4:"d"}
df = pd.DataFrame(dict1)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-68948f391692> in <module>
      1 import pandas as pd
      2 dict1 = {1:"a", 2:"b", 3:"c", 4:"d"}
----> 3 df = pd.DataFrame(dict1)

~\anaconda3\envs\Work37\lib\site-packages\pandas\core\frame.py in __init__(self, data, index, columns, dtype, copy)
    527 
    528         elif isinstance(data, dict):
--> 529             mgr = init_dict(data, index, columns, dtype=dtype)
    530         elif isinstance(data, ma.MaskedArray):
    531             import numpy.ma.mrecords as mrecords

~\anaconda3\envs\Work37\lib\site-packages\pandas\core\internals\construction.py in init_dict(data, index, columns, dtype)
    285             arr if not is_datetime64tz_dtype(arr) else arr.copy() for arr in arrays
    286         ]
--> 287     return arrays_to_mgr(arrays, data_names, index, columns, dtype=dtype)
    288 
    289 

~\anaconda3\envs\Work37\lib\site-packages\pandas\core\internals\construction.py in arrays_to_mgr(arrays, arr_names, index, columns, dtype, verify_integrity)
     78         # figure out the index, if necessary
     79         if index is None:
---> 80             index = extract_index(arrays)
     81         else:
     82             index = ensure_index(index)

~\anaconda3\envs\Work37\lib\site-packages\pandas\core\internals\construction.py in extract_index(data)
    389 
    390         if not indexes and not raw_lengths:
--> 391             raise ValueError("If using all scalar values, you must pass an index")
    392 
    393         if have_series:

ValueError: If using all scalar values, you must pass an index

要解決這個問題，就是將索引設定好，這裡有幾個解決方法，供各位參考。¶

In [3]:

import pandas as pd

# 直接在建立 DataFrame 時，設定 Index 就好。
dict1 = {1:"a", 2:"b", 3:"c", 4:"d"}
df = pd.DataFrame(dict1,index=[0])
print(df)

   1  2  3  4
0  a  b  c  d

In [5]:

import pandas as pd

# 輸入字典的時候，不要讓 value 視為內容，把 value 轉換為 list 再傳入。
dict1 = {1:["a"], 2:["b"], 3:["c"], 4:["d"]}
df = pd.DataFrame(dict1)
print(df)

   1  2  3  4
0  a  b  c  d

In [9]:

import pandas as pd

# 直接將 Key 和 value 轉換為 list 即可。
dict1 = {1:"a", 2:"b", 3:"c", 4:"d"}
df = pd.DataFrame([dict1])
print(df)

   1  2  3  4
0  a  b  c  d

In [12]:

import pandas as pd

# 使用 from_dict 將 dict 轉換為 DataFrame，在這裡將 orient = index 設定為使用字典鍵
# 可以用 .T 取得轉置資料，此與numpy的語法相同
dict1 = {1:"a", 2:"b", 3:"c", 4:"d"}
df = pd.DataFrame.from_dict(dict1, orient='index').T
print(df)

   1  2  3  4
0  a  b  c  d

Lai Tai-Yu (賴岱佑)