Create A New TA Indicator For chartSeries

Description

Functions to assist in the creation of indicators or content to be drawn on plots produced by chartSeries.

Usage

addTA(ta,
      order = NULL,
      on = NA,
      legend = "auto",
      ...)

newTA(FUN,
      tFUN,
      on = NA,
      legend.name,
      fdots = TRUE,
      cdots = TRUE,
      data.at = 1,
      ...)

Arguments

Details

Both addTA and newTA can be used to dynamically add custom content to a displayed chart.

addTA takes a series of values, either in a form coercible to xts or of the same length as the charted series has rows, and displays the results in either a new TA sub-window, or over/underlayed on the main price chart. If the object can be coerced to xts, the time values present must only be within the original series time-range. Internally a merge of dates occurs and will allow for the plotting of discontinuous series.

The order argument allows for multiple column data to be plotted in an order that makes the most visual sense.

Specifying a legend will override the standard parsing of the addTA call to attempt a guess at a suitable title for the sub-chart. Specifying this will cause the standard last value to not be printed.

The ... arg to addTA is used to set graphical parameters interpretable by lines.

newTA acts as more of a skeleton function, taking functions as arguments, as well as charting parameters, and returns a function that can be called in the same manner as the built-in TA tools, such as addRSI and addMACD. Essentially a dynamic code generator that allows for highly customizable chart tools with minimal (possibly zero) coding. It is also possible to modify the resultant code to further change behavior.

To create a new TA function with newTA certain arguments must be specified.

The FUN argument is a function symbol (or coercible to such) that is the primary filter to be used on the core-data of a chartSeries chart. This can be like most of the functions within the TTR package — e.g. RSI or EMA. The resultant object of the function call will be equal to calling the function on the original data passed into the chartSeries function that created the chart. It should be coercible to a matrix object, of one or more columns of output. By default all columns of output will be added to the chart, unless suppressed by passing the appropriately positioned type='n' as the ... arg. Note that this will not suppress the labels added to the chart.

The tFUN argument will be called on the main chart's data prior to passing it to FUN. This must be a function symbol or a character string of the name function to be called.

The on is used to identify which subchart to add the graphic to. By default, on=NA will draw the series in a new subchart below the last indicator. Setting this to either a positive or negative value will allow for the series to be super-imposed on, or under, the (sub)chart specified, respectively. A value of 1 refers to the main chart, and at present is the only location supported.

legend.name will change the main label for a new plot.

fdots and cdots enable inclusion or suppression of the ... within the resulting TA code's call to FUN, or the argument list of the new TA function, respectively. In order to facilitate user-specified graphical parameters it is usually desireable to not impose artificial limits on the end-user with constraints on types of parameters available. By default the new TA function will include the dots argument, and the internal FUN call will keep all arguments, including the dots. This may pose issues if the internal function then passes those ... arguments to a function that can't handle them.

The final argument is data.at which is the position in the FUN argument list which expects the data to be passed in at. This default to the sensible first position, though can be changed at the time of creation by setting this argument to the required value.

While the above functions are usually sufficient to construct very pleasing graphical additions to a chart, it may be necessary to modify by-hand the code produced. This can be accomplished by dumping the function to a file, or using fix on it during an interactive session.

Another item of note, with respect to newTA is the naming of the main legend label. Following addTA convention, the first ‘add’ is stripped from the function name, and the rest of the call's name is used as the label. This can be overridden by specifying legend.name in the construction of the new TA call, or by passing legend into the new TA function. Subtle differences exist, with the former being the preferred solution.

While both functions can be used to build new indicators without any understanding of the internal chartSeries process, it may be beneficial in more complex cases to have a knowledge of the multi-step process involved in creating a chart via chartSeries.

to be added...

Value

addTA will invisibly return an S4 object of class chobTA. If this function is called interactively, the chobTA object will be evaluated and added to the current chart.
newTA will return a function object that can either be assigned or evaluated. Evaluating this function will follow the logic of any standard addTA-style call, returning invisibly a chobTA object, or adding to the chart.

Note

Both interfaces are meant to fascilitate custom chart additions. addTA is for adding any arbitrary series to a chart, where-as newTA works with the underlying series with the main chart object. The latter also acts as a dynamic TA skeleton generation tool to help develop reusable TA generation code for use on any chart.

Author(s)

Jeffrey A. Ryan

See Also

chartSeries, TA, chob, chobTA

Examples

## Not run: 
getSymbols('SBUX')
barChart(SBUX)
addTA(EMA(Cl(SBUX)), on=1, col=6)
addTA(OpCl(SBUX), col=4, type='b', lwd=2)
# create new EMA TA function
newEMA <- newTA(EMA, Cl, on=1, col=7)
newEMA()
newEMA(on=NA, col=5)
## End(Not run)