Implementing an indicator - I

At this point, it's time to start getting into the mechanics of implementing an indicator within the scope of the quantstrat library. In this exercise you will learn how to add an indicator to your strategy. For this exercise you will use the strategy you created in earlier exercies, strategy.st. For your first indicator, you will add a 200-day simple moving average.

To add an indicator to your strategy, you will use the add.indicator() function. This function takes a series of arguments: the strategy, the name of the indicator function, the arguments for the indicator function, and the label for the function output.

In detail, the add.indicator() function tells quantstrat you wish to add an indicator. The strategy argument asks you to provide the name of your strategy. Next, the name argument asks for a name of a function, such as SMA, RSI, and so on, in quotes. The arguments argument asks for the arguments to the named function. For instance, if your function name was SMA, the arguments argument will be the arguments to the SMA function. Quantstrat needs these arguments provided in the form of a list.

Importantly, when referencing dynamic market data in your add.indicator() call, you need to make sure that mktdata is included inside the quote function. mktdata is created inside quantstrat and will change depending on the instrument quantstrat uses at the time. Therefore, this object needs to be encapsulated in the quote function so that it can dynamically change over the course of running your strategy.

Instructions

Add a 200-day SMA to your strategy (strategy.st), using the add.indicator() function.
Provide the name of the the simple moving function to the name argument.
Provide the proper argument values to create a lookback period of 200 days.
Label your indicator "SMA200".
Note that these lines are indented because they are all part of the same add.indicator() call.

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