How can I pass individual `curvature` arguments in `ggplot2` `geom_curve` function?

Question

I have a df with two curve definitions, each consists of two points and a curvature value. The goal is to plot two individual curves using ggplot2

Answer 1

You could use a for loop to build up your ggplot call as a text string and evaluate the string once the for loop finishes.

graphString <- "ggplot(df) "
for(i in 1:nrow(df)){
  newCurve <- paste(" + geom_curve(data = df[",i,", ], aes(x = x, y = y, xend = xend, yend = yend), curvature = df$curvature[",i,"])", sep="")
  graphString <- paste(graphString, newCurve,sep="")
}

eval(parse(text = graphString))

Answer 2

update

You might split your data first and then use lapply to iterate over the resulting list which we'll feed to the data argument of geom_curve()

df2 <- data.frame(x = c(0,.2), y = c(0,.3), xend = c(1,.4), yend = c(1,.6), curvature = c(-.2,.4))
ggplot() + 
  lapply(split(df2, 1:nrow(df)), function(dat) {
    geom_curve(data = dat, aes(x = x, y = y, xend = xend, yend = yend), curvature = dat["curvature"]) }
  )

original ansewr

curvature is not an aesthetic, as you have noted. You can add a list to ggplot(), to get it work

df <- data.frame(x = c(0,0), y = c(0,0), xend = c(1,1), yend = c(1,1), curvature = c(-.2,.8))
ggplot(df) + 
  lapply(df$curvature, function(i) {
    geom_curve(aes(x = x, y = y, xend = xend, yend = yend), curvature = i) }
    )

From help("+.gg")

What can you add?

...

You can also supply a list, in which case each element of the list will be added in turn.

---

If you have other parameters that you want to show in your plot - each line might be coloured differently, is of different size etc. - use Map

Modified data

df1 <- data.frame(x = c(0,0), y = c(0,0), xend = c(1,1), yend = c(1,1), curvature = c(-.2,.8),
                  colour = c("red", "blue"))

Plot

ggplot(df1) + 
  Map(function(i, col) {
    geom_curve(aes(x = x, y = y, xend = xend, yend = yend), curvature = i, colour = col) },
    i = df1$curvature, col = df1$colour
  )

Result