polar coordinates

[cpsievert]

There's some useful math stuff here -- https://github.com/hadley/ggplot2/blob/5f4af9eafed9cbd7e3c84285fe3c9047f1ccb17d/tests/testthat/test-coord-polar.r

dat <- data.frame(
    theta = c(0, 2*pi,   2,   6, 6, 1,    1,  0),
    r     = c(0,    0, 0.5, 0.5, 1, 1, 0.75, .5)
)

ggplot(dat, aes(x = theta, y = r)) + geom_path() +
    geom_point(alpha = 0.3) + coord_polar()

[cpsievert]

We'll have to add something like this ggplotly.R

if (inherits(p$coordinates, "CoordPolar")) {
    # add angularaxis to layout and warn about no subplot availiability
}

https://plot.ly/javascript/polar-chart/

[cpsievert]

Closing in favor of #878