提取ARIMA特性

Question

从auto.arima()打印合适的模型对象包括一行，如

有漂移的ARIMA(2，1，0)

这将是一个很好的项目，包括在横幅(或其他)输出，说明拟合的模式。有可能把这条线作为块提取出来吗？在这一点上，我所做的最好是从arma分量中提取适当的顺序(可能从拟合模型的系数的名称(例如，“具有漂移”或“具有非零均值”)中提取适当的阶次。

# R 3.0.2 x64 on Windows, forecast 5.3 
library(forecast)  
y <- ts(data = c(-4.389, -3.891, -4.435, -5.403, -2.501, -1.858, -4.735, -1.085, -2.701, -3.908, -2.520, -2.009, -6.961, -2.891, -0.6791, -1.459, -3.210, -2.178, -1.972, -1.207, -1.376, -1.355, -1.950, -2.862, -3.475, -1.027, -2.673, -3.116, -1.290, -1.510, -1.736, -2.565, -1.932, -0.8247, -2.067, -2.148, -1.236, -2.207, -1.120, -0.6152), start = 1971, end = 2010)  
fm <- auto.arima(y)  
fm  

# what I want is the line: "ARIMA(2,1,0) with drift`"  

str(fm)  
paste("ARIMA(", fm$arma[1], ",", fm$arma[length(fm$arma)-1], ",", fm$arma[2], ") with ",intersect("drift", names(fm$coef)), sep = "")

Answer 1

检查auto.arima函数时，我注意到它内部调用了另一个函数，名为arima.string。

然后我做了：

getAnywhere(arima.string)

产出如下：

A single object matching ‘arima.string’ was found
It was found in the following places
namespace:forecast
with value

function (object) 
{
order <- object$arma[c(1, 6, 2, 3, 7, 4, 5)]
result <- paste("ARIMA(", order[1], ",", order[2], ",", order[3], 
    ")", sep = "")
if (order[7] > 1 & sum(order[4:6]) > 0) 
    result <- paste(result, "(", order[4], ",", order[5], 
        ",", order[6], ")[", order[7], "]", sep = "")
if (is.element("constant", names(object$coef)) | is.element("intercept", 
    names(object$coef))) 
    result <- paste(result, "with non-zero mean")
else if (is.element("drift", names(object$coef))) 
    result <- paste(result, "with drift        ")
else if (order[2] == 0 & order[5] == 0) 
    result <- paste(result, "with zero mean    ")
else result <- paste(result, "                  ")
return(result)

}

然后，我复制了函数代码并将其粘贴到一个新函数中，我将其命名为arima.string1。

arima.string1(fm)

# [1] "ARIMA(2,1,0) with drift        "

Answer 2

今天，我发现我寻找的文本块也存储在拟合模型对象的预测中：

forecast(fm)$method  

感谢费尔南多恰当地标记了我的问题，感谢Davide提供了一对有用的见解-- getAnywhere()和arima.string()，可以修改了。