SIM-AMZN

options("getSymbols.yahoo.warning"=FALSE)

suppressWarnings(suppressMessages(library(quantmod)))

amazon = getSymbols("AMZN", auto.assign=F, from = "2018-01-01", to = "2018-04-01")

## 'getSymbols' currently uses auto.assign=TRUE by default, but will
## use auto.assign=FALSE in 0.5-0. You will still be able to use
## 'loadSymbols' to automatically load data. getOption("getSymbols.env")
## and getOption("getSymbols.auto.assign") will still be checked for
## alternate defaults.
## 
## This message is shown once per session and may be disabled by setting 
## options("getSymbols.warning4.0"=FALSE). See ?getSymbols for details.

#plot(as.ts(amazon$AMZN.Open))

# functions to explore unprocessed xts from quantmod
 chartSeries(amazon, type = "line")

# acf and pacf to get an idea about autocorrelation
library(forecast)
ggtsdisplay(amazon$AMZN.Open)

# Arima model
amazonarima = auto.arima(amazon$AMZN.Open, stepwise = T, approximation = F, trace = T); amazonarima

## 
##  ARIMA(2,1,2) with drift         : 599.3494
##  ARIMA(0,1,0) with drift         : 595.3083
##  ARIMA(1,1,0) with drift         : 597.481
##  ARIMA(0,1,1) with drift         : 597.445
##  ARIMA(0,1,0)                    : 593.982
##  ARIMA(1,1,1) with drift         : 599.3131
## 
##  Best model: ARIMA(0,1,0)

## Series: amazon$AMZN.Open 
## ARIMA(0,1,0) 
## 
## sigma^2 estimated as 1127:  log likelihood=-295.96
## AIC=593.91   AICc=593.98   BIC=596.01

plot(forecast(amazonarima, h = 20)) # next 20 days

# Ets model - exponential smoothing
amazonets <- ets(amazon$AMZN.Open)

# Forecast ets
plot(forecast(amazonets, h = 20)) #next 20 days

no clear trend, no seasonality. Therefore price not predictable.