Python : compare data frame row value with previous row value

Question

I am trying to create a new Column by comparing the value row with its previous value error that I get is ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). I have checked the data type of columns. All of them are float64

But I am getting an error CODE:

    cols=['High', 'Low', 'Open', 'Volume', "Adj Close"]
    df = df.drop(columns = cols)
    df['EMA60'] = df['Close'].ewm(span=60, adjust=False).mean()
    df['EMA100'] = df['Close'].ewm(span=100, adjust=False).mean()
    df['MACD_60_100'] = df['EMA60'] - df['EMA100']
    df['SIGNAL_60_100'] = df['MACD_60_100'].ewm(span=9, adjust=False).mean()
    df['HIST_60_100'] = df['MACD_60_100'] - df['SIGNAL_60_100'] # Histogram
    df = df.iloc[1: , :]  # Delete first row in DF as it contains NAN
    print(df.dtypes)
    print (df)
    if df[df['HIST_60_100'] > df['HIST_60_100'].shift(+1)]: # check if the valus is > previous row value
        df['COLOR-60-100'] = "GREEN"
    else:
        df['COLOR-60-100'] = "RED"

    print(df.to_string())

ERROR:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_10972/77395577.py in <module>
     32 
     33 
---> 34   get_data_from_yahoo(symbol+".NS")
     35 
     36   # df.to_excel(sheetXls, index=False)

~\AppData\Local\Temp/ipykernel_10972/520355426.py in get_data_from_yahoo(symbol, interval, start, end)
     26     print(df.dtypes)
     27     print (df)
---> 28     if df[df['HIST_60_100'] > df['HIST_60_100'].shift(+1)]:
     29         df['COLOR-60-100'] = "GREEN"
     30     else:

~\AppData\Roaming\Python\Python39\site-packages\pandas\core\generic.py in __nonzero__(self)
   1327 
   1328     def __nonzero__(self):
-> 1329         raise ValueError(
   1330             f"The truth value of a {type(self).__name__} is ambiguous. "
   1331             "Use a.empty, a.bool(), a.item(), a.any() or a.all()."

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

Timeless · Accepted Answer · 2022-12-04 18:34:32Z

1

No need for an if.. else statement here. You can use numpy.where instead.

numpy.where(condition, [x, y, ]/)

Replace this :

if df[df['HIST_60_100'] > df['HIST_60_100'].shift(+1)]: # check if the valus is > previous row value
    df['COLOR-60-100'] = "GREEN"
else:
    df['COLOR-60-100'] = "RED"

By this :

df['COLOR-60-100'] = np.where(df['HIST_60_100'].gt(df['HIST_60_100'].shift(1), "GREEN", "RED")

answered Dec 4, 2022 at 18:34

Timeless

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