r - Using geom_segment with coord_polar

Question

I want to do something similar to the answer in this post, but with `geom_segment()` instead of `geom_path()` because now I want to add arrows to my lines. Setup: ``` example <- data.frame(r=c(5,4,3),theta=c(0.9,1.1,0.6)) is.linear.polar2 <- function(x) TRUE coord_polar2 <- coord_polar(theta="y", start = 3/2*pi, direction=-1) class(coord_polar2) <- c("polar2", class(coord_polar2)) myplot <- ggplot(example, aes(r, theta)) + geom_point(size=3.5) + scale_x_continuous(breaks=seq(0,max(example$r)), lim=c(0, max(example$r))) + scale_y_continuous(breaks=round(seq(0, 2*pi, by=pi/4),2), expand=c(0,0), lim=c(0,2*pi)) + geom_text(aes(label=rownames(example)), size=4.4, hjust=0.5, vjust=-1) myplot + coord_polar2 + geom_path() ``` I want a plot that looks like this, but with arrows in the direction of the next point in the sequence. These are my attempts: ``` myplot + coord_polar2 + geom_segment(data=example,aes(x=r, y=theta, xend=c(tail(r, n=-1), NA), yend=c(tail(theta, n=-1), NA)), arrow=arrow(l…

Accepted Answer

Well, this solution is even hackier than the answer to your first question. Instead of using `geom_segment` I use `geom_path`, but this will produce only the last arrow, so we will add the `group` aesthetic to connect segments one by one. This means our original data frame has to be slightly modified:

```
tweak_data <- function(df) 
{
  if (nrow(df) == 1) return(df)
  idx_x2 <- c(1, rep(2:(nrow(df) - 1), each=2), nrow(df))
  gr <- rep(seq.int(nrow(df) - 1), each=2)
  df_res <- data.frame(r = df$r[idx_x2], theta = df$theta[idx_x2], 
                       label = rownames(df)[idx_x2], group = gr)
  df_res
}

example_tw <- tweak_data(example)
myplot2 <- ggplot(example2, aes(r, theta)) + geom_point(size=3.5) +
  scale_x_continuous(breaks=seq(0,max(example$r)), lim=c(0, max(example$r))) + 
  scale_y_continuous(breaks=round(seq(0, 2*pi, by=pi/4), 2), 
                     expand=c(0, 0), lim=c(0, 2*pi)) +
  geom_text(aes(label=label), size=4.4, hjust=0.5, vjust=-1)
myplot2 + coord_polar2 + 
  geom_path(aes(group=group), arrow=arrow(length=unit(0.3,"cm"), type="closed"))
```

r - Using geom_segment with coord_polar

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