我试图使用Python和Statsmodels来理解ARIMA预测。具体而言,为了使ARIMA算法起作用,需要通过差分(或类似的方法)使数据变得平稳。问题是:在残差预测完成后,如何反转差分以回到包括趋势和季节性的预测中?
(我看到了一个类似的问题here,但遗憾的是没有发布答案。)
到目前为止,我已经完成了以下工作(基于Magnus Vilhelm Persson和Luiz Felipe Martins的《掌握Python数据分析》最后一章中的示例)。数据来自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)
生成的图表很令人满意,但是没有包含趋势和季节性信息。我该如何反差分以恢复趋势/季节性?残差图
predict
有一个typ='level'
关键字。对于季节性数据,SARIMAX更合适。 - Josef