ggvis: add size property to a line

Question

Just getting started with ggvis. Not a particularly interesting or general question I'm afraid, but its is not obvious to me how to add a size property to a line. In particular, how would I replicate the following plot using ggvis?

library(ggplot2)

df <- data.frame(
  id = c(1,1,1,2,2,2,2),
  x  = c(1,2,3,1,2,3,4),
  y  = c(2,3,4,1,1,2,3)
)

ggplot(df, aes(x, y, colour = as.factor(id), size = id)) +
  geom_line()

Also, could someone with a high enough reputation create a ggvis tag? Cheers.

Answer 1

The following:

library(ggvis)

gg <- ggvis(df, props(~x, ~y, stroke = ~factor(id)))
gg <- gg + layer_line(props(strokeWidth := ~id*4))
gg

produces:

I had to tweak the multiplier for the strokeWidth to get it to be a bit thicker, but that should be a good starting point for you. Remember ggivs is based on Vega so getting familiar with the terminology in that new graphics grammar is going to almost be a requirement to understand how to "think" in ggvis.

Here's an example of doing this more properly (and more ggplot2-like with scale_quantitative:

gg <- ggvis(df, props(~x, ~y, stroke = ~factor(id)))
gg <- gg + layer_line(props(strokeWidth = ~id)) 
gg <- gg + scale_quantitative("strokeWidth",
                              trans="linear", 
                              domain=range(df$id), 
                              range=c(1,10))
gg

Doing a ?scale_quantitative or reviewing the "scales" online examples should give you a good idea of your options for getting the desired effect.

I also should point out the use of "=" vs ":=" in the second example. From the ggvis site:

The props() function uses the = operate for mapping (scaled), and the := operator for setting (unscaled). It also uses the ~ operator to indicate that an expression should be evaluated in the data (and in ggvis, the data can change); without the ~ operator, the expression is evaluated immediately in the current environment.