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

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)