[英]How to invert differencing in a Python statsmodels ARIMA forecast?
我正試圖用Python和Statsmodels來圍繞ARIMA預測。 具體而言,為了使ARIMA算法起作用,需要通過差分(或類似方法)使數據靜止。 問題是:在進行剩余預測后,如何在差異化之后反轉差異,以回歸預測,包括趨勢和季節性差異?
(我在這里看到了一個類似的問題,但是唉,沒有發布任何答案。)
這是我到目前為止所做的事情(基於掌握Python數據分析的最后一章中的例子,Magnus Vilhelm Persson; Luiz Felipe Martins)。 數據來自DataMarket 。
%matplotlib inline
import matplotlib.pyplot as plt
import pandas as pd
from statsmodels import tsa
from statsmodels.tsa import stattools as stt
from statsmodels.tsa.seasonal import seasonal_decompose
from statsmodels.tsa.arima_model import ARIMA
def is_stationary(df, maxlag=15, autolag=None, regression='ct'):
"""Test if df is stationary using Augmented
Dickey Fuller"""
adf_test = stt.adfuller(df,maxlag=maxlag, autolag=autolag, regression=regression)
adf = adf_test[0]
cv_5 = adf_test[4]["5%"]
result = adf < cv_5
return result
def d_param(df, max_lag=12):
d = 0
for i in range(1, max_lag):
if is_stationary(df.diff(i).dropna()):
d = i
break;
return d
def ARMA_params(df):
p, q = tsa.stattools.arma_order_select_ic(df.dropna(),ic='aic').aic_min_order
return p, q
# read data
carsales = pd.read_csv('data/monthly-car-sales-in-quebec-1960.csv',
parse_dates=['Month'],
index_col='Month',
date_parser=lambda d:pd.datetime.strptime(d, '%Y-%m'))
carsales = carsales.iloc[:,0]
# get components
carsales_decomp = seasonal_decompose(carsales, freq=12)
residuals = carsales - carsales_decomp.seasonal - carsales_decomp.trend
residuals = residuals.dropna()
# fit model
d = d_param(carsales, max_lag=12)
p, q = ARMA_params(residuals)
model = ARIMA(residuals, order=(p, d, q))
model_fit = model.fit()
# plot prediction
model_fit.plot_predict(start='1961-12-01', end='1970-01-01', alpha=0.10)
plt.legend(loc='upper left')
plt.xlabel('Year')
plt.ylabel('Sales')
plt.title('Residuals 1960-1970')
print(arimares.aic, arimares.bic)
由此產生的情節令人滿意,但不包括趨勢,季節性信息。 如何反轉差分以重新獲得趨勢/季節性? 剩余情節
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