代码返回没有索引的空数据框

Question

我正在尝试使用每日股票数量的历史数据制作一个数据框，这些数据随着 Nifty 50 指数各自的交易量而上涨和下跌。 作为 python 新手，我在处理 pandas 数据帧和条件时遇到了麻烦。

下面是我写的代码，但是有很多问题：

1. df.index = data.index 错误：ValueError：长度不匹配：预期轴有 0 个元素，新值有 248 个元素

2. 如果我注释掉上面设置空数据帧索引的行，代码运行并在最后给出一个空数据帧。

   #setting default dates
   end_date = date.today()
   start_date = end_date - timedelta(365)
   
   #Deriving the names of 50 stocks in Nifty 50 Index
   nifty_50 = pd.read_html('https://en.wikipedia.org/wiki/NIFTY_50')
   
   nifty50_symbols = nifty_50[1][1]
   
   df = pd.DataFrame(columns = {'Advances','Declines','Adv_Volume','Dec_Volume'})
   
   
   for x in nifty50_symbols:
       data = nsepy.get_history(symbol = x, start=start_date, end=end_date)
       sclose = data['Close']
       sopen = data['Open']
       svol = data['Volume']
   
   
    ##    df.index = data.index
   
    ##   for i in df.index: --- since df.index was commented out it's value was nill
       for i in data.index:
           if sclose > sopen:
               df['Advances'] = df['Advances'] + 1
               df['Adv_Volume'] = df['Adv_Volume'] + svol
   
           elif sopen > sclose:
               df['Declines'] = df['Declines'] + 1
               df['Dec_Volume'] = df['Dec_Volume'] + svol
   
   
   print(df.tail())
   

输出：

Empty DataFrame
Columns: [Dec_Volume, Declines, Advances, Adv_Volume]
Index: []

编辑：找到了代码给出空数据框的原因，因为 df.index 为空，因此从未触发过 if 语句。当我将该部分更改为 data.index 时，如果触发了语句。但是现在我不知道如何使用 IF 语句，因为它给出了错误：

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

EDIT2：在 Akshay Nevrekar 的帮助下更新了代码：最后仍然得到一个空数据框。此外，我必须将 DF 的索引设置为 data.index 中的日期，以便以后可以将 Advances/declines 与它们各自的日期联系起来。

#setting default dates
end_date = date.today()
start_date = end_date - timedelta(365)

#Deriving the names of 50 stocks in Nifty 50 Index
nifty_50 = pd.read_html('https://en.wikipedia.org/wiki/NIFTY_50')

nifty50_symbols = nifty_50[1][1]

df = pd.DataFrame(columns = {'Advances','Declines','Adv_Volume','Dec_Volume'})


for x in nifty50_symbols:
    data = ns.get_history(symbol = x, start=start_date, end=end_date)
##    sclose = data['Close']
##    sopen = data['Open']
##    svol = data['Volume']

##    df.index = data.index

    for i in data.index:
        sclose=data.loc[i]['Close']
        sopen=data.loc[i]['Open']
        svol = data.loc[i]['Volume']

        if sclose > sopen :
            df['Advances'] = df['Advances'] + 1
            df['Adv_Volume'] = df['Adv_Volume'] + svol

        elif sopen > sclose :
            df['Declines'] = df['Declines'] + 1
            df['Dec_Volume'] = df['Dec_Volume'] + svol



print(df

)

Answer 1

您正在创建一个空数据框。

df = pd.DataFrame(columns = {'Advances','Declines','Adv_Volume','Dec_Volume'})

所以df.index 将是空的并且

 for i in df.index:
    if sclose > sopen:
        df['Advances'] = df['Advances'] + 1
        df['Adv_Volume'] = df['Adv_Volume'] + svol

    elif sopen > sclose:
        df['Declines'] = df['Declines'] + 1
        df['Dec_Volume'] = df['Dec_Volume'] + svol

你上面的for循环永远不会运行。这就是你得到一个空数据框的原因。

编辑：编辑后，我建议您在 for 循环中声明 sclose 和 sopen 变量。您正在将整列分配给变量而不是单个值。

for i in data.index:
    sclose=data.iloc[i]['Close']
    sopen=data.iloc[i]['Open']
    svol=data.iloc[i]['Volume']

    if sclose > sopen:
       df.loc[i]['Advances'] = df.loc[i]['Advances'] + 1
       df.loc[i]['Adv_Volume'] = df.loc[i]['Adv_Volume'] + svol
    elif sopen > sclose:
       df.loc[i]['Declines'] = df.loc[i]['Declines'] + 1
       df.loc[i]['Dec_Volume'] = df.loc[i]['Dec_Volume'] + svol