如何用 Python 中的公式替换查看多个先前值的循环

Question

我的问题我有一个循环，它使用基于其他列的值的公式或列中的前一个值创建列，具体取决于条件（“从新低开始的天数 == 0”）。在庞大的数据集上它真的很慢，所以我想摆脱循环并找到一个更快的公式。当前工作代码import numpy as npimport pandas as pdcsv1 = pd.read_csv('stock_price.csv', delimiter = ',')df = pd.DataFrame(csv1)for x in range(1,len(df.index)):    if df["days from new low"].iloc[x] == 0:        df["mB"].iloc[x] = (df["RSI on new low"].iloc[x-1] - df["RSI on new low"].iloc[x]) / -df["days from new low"].iloc[x-1]    else:        df["mB"].iloc[x] = df["mB"].iloc[x-1]df输入数据和预期输出RSI on new low,days from new low,mB0,22,029.6,0,1.329.6,1,1.329.6,2,1.329.6,3,1.329.6,4,1.321.7,0,-2.021.7,1,-2.021.7,2,-2.021.7,3,-2.021.7,4,-2.021.7,5,-2.021.7,6,-2.021.7,7,-2.021.7,8,-2.021.7,9,-2.025.9,0,0.525.9,1,0.525.9,2,0.523.9,0,-1.023.9,1,-1.0尝试解决方案def mB_calc (var1,var2,var3):    df[var3]= np.where(df[var1] == 0, df[var2].shift(1) - df[var2] / -df[var1].shift(1) , "")    return dfdf = mB_calc('days from new low','RSI on new low','mB')  首先，它给了我这个“TypeError：不能将序列乘以'float'类型的非整数”，其次我不知道如何将“ffill”合并到公式中。知道我怎么能做到吗？干杯!

Answer 1

试试这个：

df["mB_temp"] = (df["RSI on new low"].shift() - df["RSI on new low"]) / -df["days from new low"].shift()

df["mB"] = df["mB"].shift()

df["mB"].loc[df["days from new low"] == 0]=df["mB_temp"].loc[df["days from new low"] == 0]

df.drop(["mB_temp"], axis=1)

并与np.where：

df["mB"] = np.where(df["days from new low"]==0, df["RSI on new low"].shift() - df["RSI on new low"]) / -df["days from new low"].shift(), df["mB"].shift())