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In vanilla plotting, it is possible to use a polygon call in the panel.first argument to plot to highlight a background region. Is it possible to do the same in ggplot2? Can it be done while preserving the gridlines?
eg:
# plot hp and wt for mtcars data, highlighting region where hp/wt ratio < 35
with(mtcars,plot(hp,wt,
panel.first=polygon(c(0,0,max(wt)*35),c(0,max(wt),max(wt)),
col="#d8161688",border=NA)))
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We can use the new data frame containing the data points to be highlighted to add another layer of geom_point(). Note that we have two geom_point(), one for all the data and the other for with data only for the data to be highlighted.
%>% is a pipe operator reexported from the magrittr package. Start by reading the vignette. Adding things to a ggplot changes the object that gets created. The print method of ggplot draws an appropriate plot depending upon the contents of the variable.
ggplot2 allows you to do data manipulation, such as filtering or slicing, within the data argument.
Yes, that's possible with ggplot2. To preserve the visibility of grid lines you can use alpha transparency. Note that, in general, the order in which geoms and stats are applied matters.
tmp <- with(mtcars, data.frame(x=c(0, 0, max(wt)*35), y=c(0, max(wt), max(wt))))
ggplot(mtcars, aes(hp, wt)) +
geom_polygon(data=tmp, aes(x, y), fill="#d8161688") +
geom_point()
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