Question

我正在尝试制作一个数据框，其中包含每日库存数量的历史数据，以及它们各自的Nifty 50指数的上升和下降。作为python的新手，我无法处理pandas数据帧和条件。

以下是我编写的代码，但它有很多问题：

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

如果我在上面的行中注释掉我设置空数据帧的索引，代码就会运行并在最后给出一个空的Dataframe。

#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: []

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的数据帧。另外，我必须将DF的索引设置为data.index中的日期，以便稍后我可以将Advances / declines与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将为空且

 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

您在 for循环之上将永远不会运行。这就是为什么你得到一个空的数据帧。

编辑：编辑后我建议您在for循环中声明sclose和sopen变量。您将整个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

代码返回没有索引

1 个答案: