Rotate x-axis text when using coord_polar()

Question

I have a scatter-plot with many values on a polar axis - coord_polar(). The resulting graph has crowded text because the text is always aligned with the bottom of the page.

Is it possible to place the text so that it is printed radially along the polar x-axis?

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Edited to provide an example:

qplot(data=presidential, name,end) + coord_polar()

In the presidential case I would like to see the presidential names angled to align with the axis/spoke they are on. Below is an example of the graph I am working on where the x axis is categorical and the y-axis is a continuous variable (similar to the example).

Answer 1

I understand this is an old topic, but I found a better solution for this problem, inspired from baptise's comment:

ggplot(data, aes(x=someId, y=someValue)) +
  geom_point() + 
  coord_polar() +
  theme(axis.text.x = element_text(
    angle= -90 - 360 / length(unique(data$someId)) * seq_along(data$someId)
    )
  )

Answer 2

The answer by Yoplait helps a lot, but still does not solve the issue of having to read upside down in half of the graph. An extention of the idea that this poster proposes is as follows.

First prepare the angle vector, making sure we split the graph in two:

sequence_length = length(unique(data$someId))
first_sequence = c(1:(sequence_length%/%2)) 
second_sequence = c((sequence_length%/%2+1):sequence_length) 
first_angles = c(90 - 180/length(first_sequence) * first_sequence)
second_angles = c(-90 - 180/length(second_sequence) * second_sequence)

And now we can append the angle vectors to make the actual graph:

ggplot(data, aes(x=someId, y=someValue)) +
  geom_point() + 
  coord_polar() +
  theme(axis.text.x = element_text(
    angle= c(first_angles,second_angles)
    )
  )

Answer 3

here is a not elegant example of the coordinate:

CoordPolar2 <- proto(CoordPolar, {
  objname <- "polar2"
  guide_foreground <- function(., details, theme) {
    theta <- .$theta_rescale(details$theta.major, details)
    labels <- details$theta.labels

    # Combine the two ends of the scale if they are close
    theta <- theta[!is.na(theta)]
    ends_apart <- (theta[length(theta)] - theta[1]) %% (2*pi)
    if (ends_apart < 0.05) {
      n <- length(labels)
      if (is.expression(labels)) {
        combined <- substitute(paste(a, "/", b), 
          list(a = labels[[1]], b = labels[[n]]))
      } else {
        combined <- paste(labels[1], labels[n], sep="/")
      }
      labels[[n]] <- combined
      labels <- labels[-1]
      theta <- theta[-1]
    }

    grobTree(
      if (length(labels) > 0) {
        lab <- theme_render(
          theme, "axis.text.x", 
          labels, 0.45 * sin(theta) + 0.5, 0.45 * cos(theta) + 0.5,
          hjust = 0.5, vjust = 0.5,
          default.units="native"
        )
        lab$rot <- (pi/2 - theta) / pi * 180
        lab
      },
      theme_render(theme, "panel.border")
    )
  }
})

coord_polar2 <- CoordPolar2$build_accessor()

p <- qplot(data=presidential, name,end) + coord_polar2()
print(p)