rCharts Polychart: Adding horizontal or vertical lines to a plot

Question

I'm having some trouble understanding how to customize graphs using the rPlot function in the rCharts Package. Say I have the following code

#Install rCharts if you do not already have it
#This will require devtools, which can be downloaded from CRAN
require(devtools)
install_github('rCharts', 'ramnathv')

#simulate some random normal data
x <- rnorm(100, 50, 5)
y <- rnorm(100, 30, 2)

#store in a data frame for easy retrieval
demoData <- data.frame(x,y)

#generate the rPlot Object
demoChart <- rPlot(y~x, data = demoData, type = 'point')

#return the object // view the plot
demoChart

This will generate a plot and that is nice, but how would I go about adding horizontal lines along the y-axis? For example, if I wanted to plot a green line which represented the average y-value, and then red lines which represented +/- 3 standard deviations from the average? If anybody knows of some documentation and could point me to it then that would be great. However, the only documentation I could find was on the polychart.js (https://github.com/Polychart/polychart2) and I'm not quite sure how to apply this to the rCharts rPlot function in R.

I have done some digging and I feel like the answer is going to have something to do with adding/modifying the layers parameter within the rPlot object.

#look at the slots in this object
demoChart$params$layers

#doing this will return the following output (which will be different for
#everybody because I didn't set a seed). Also, I removed rows 6:100 of the data.

demoChart$params$layers
[[1]]
[[1]]$x
[1] "x"

[[1]]$y
[1] "y"

[[1]]$data
       x        y
1   49.66518 32.75435
2   42.59585 30.54304
3   53.40338 31.71185
4   58.01907 28.98096
5   55.67123 29.15870


[[1]]$facet
NULL

[[1]]$type
[1] "point"

If I figure this out I will post a solution, but I would appreciate any help/advice in the meantime! I don't have much experience playing with objects in R. I feel like this is supposed to have some similarity to ggplot2 which I also don't have much experience with.

Thanks for any advice!

Answer 1

You can overlay additional graphs onto your rCharts plot using layers. Add values for any additional layers as columns on to your original data.frame. copy_layer lets you use the values from the data.frame in the extra layers.

# Regression Plots using rCharts
require(rCharts)

mtcars$avg <- mean(mtcars$mpg)
mtcars$sdplus <- mtcars$avg + sd(mtcars$mpg)
mtcars$sdneg <-  mtcars$avg - sd(mtcars$mpg)

p1 <- rPlot(mpg~wt, data=mtcars, type='point')

p1$layer(y='avg', copy_layer=T, type='line', color=list(const='red'))
p1$layer(y='sdplus', copy_layer=T, type='line', color=list(const='green'))
p1$layer(y='sdneg', copy_layer=T, type='line', color=list(const='green'))

p1 

Here are a couple of examples: one from the main rCharts website and the other showing how to overlay a regression line.