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 geom_curve (or an alternative).

I can generate my expected output using:

df <- data.frame(x = c(0,.2), y = c(0,.3), xend = c(1,.4), yend = c(1,.6), curvature = c(-.2,.4))
ggplot(df) + geom_curve(data = df[1, ], aes(x = x, y = y, xend = xend, yend = yend), curvature = df$curvature[1]) + geom_curve(data = df[2, ], aes(x = x, y = y, xend = xend, yend = yend), curvature = df$curvature[2])

But this is not really a solution, since in my real case I have lot more curves (and I don't know how many in advance).

How can I pass an individual curvature argument to the geom_curve call?

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I tried:

df <- data.frame(x = c(0,0), y = c(0,0), xend = c(1,1), yend = c(1,1), curvature = c(-.2,.8))
library(ggplot2)
ggplot(df) + geom_curve(aes(x = x, y = y, xend = xend, yend = yend, curvature = curvature))

This plots both curves on top of each other and throws an additional warning:

Warning: Ignoring unknown aesthetics: curvature

---

So I tried:

ggplot(df) + geom_curve(aes(x = x, y = y, xend = xend, yend = yend), curvature = curvature)

This throws an error:

Error in layer(data = data, mapping = mapping, stat = stat, geom = GeomCurve, : object 'curvature' not found

---

So I tried to explicitly pass the curvature colon:

ggplot(df) + geom_curve(aes(x = x, y = y, xend = xend, yend = yend), curvature = df$curvature)

This as well throws an error:

Error in seq.default(0, dir * maxtheta, dir * maxtheta/(ncp + 1)) :
'to' muss Länge 1 haben In addition: Warning messages: 1: In if (curvature == 0) { : the condition has length > 1 and only the first element will be used 2: In if (curvature > 0) hand <- "right" else hand <- "left" : the condition has length > 1 and only the first element will be used

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From @markus' solution I learned, that we can pass lists to a ggplot object, so I tried:

ggplot(df) + 
  lapply(df$curvature, function(i) {
    geom_curve(aes(x = x, y = y, xend = xend, yend = yend), curvature = i) }
  )

But this plots each curve with both curvature argument:

---

How can I pass that curvature argument individually for each row?

Fusiform

Answer 1

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.

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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

Valval

Might also be helpful to apply over groups rather than rows depending on application – Diacritical

Using the updated version of your code and ggplot2_3.5.1, I got an error. I was applying it to an sf object, so had to change dat["curvature"] to dat$curvature. – Brunobruns

Answer 2

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))

Tinkling

What would be the advantage of this? Cause I guess it will still call geom_curve nrow(df) times – Could

Answer 3

The R package linkET https://github.com/Hy4m/linkET has a function geom_curve2(). You can try this function.

Horsefly

While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review – Brunobruns