How to make gradient color filled timeseries plot in R

Question

How to fill area under and above (sp)line with gradient color?

This example has been drawn in Inkscape - BUT I NEED vertica

Answer 1

This is a terrible way to trick ggplot into doing what you want. Essentially, I make a giant grid of points that are under the curve. Since there is no way of setting a gradient within a single polygon, you have to make separate polygons, hence the grid. It will be slow if you set the pixels too low.

gen.bar <- function(x, ymax, ypixel) {
  if (ymax < 0) ypixel <- -abs(ypixel)
  else ypixel <-  abs(ypixel)
  expand.grid(x=x, y=seq(0,ymax, by = ypixel))
}

# data must be in x order.
find.height <- function (x, data.x, data.y) {
  base <- findInterval(x, data.x)
  run <- data.x[base+1] - data.x[base]
  rise <- data.y[base+1] - data.y[base]
  data.y[base] + ((rise/run) * (x - data.x[base]))
}

make.grid.under.curve <- function(data.x, data.y, xpixel, ypixel) {
  desired.points <- sort(unique(c(seq(min(data.x), max(data.x), xpixel), data.x)))
  desired.points <- desired.points[-length(desired.points)]

  heights <- find.height(desired.points, data.x, data.y)
  do.call(rbind, 
          mapply(gen.bar, desired.points, heights, 
                 MoreArgs = list(ypixel), SIMPLIFY=FALSE))
}

xpixel = 0.01
ypixel = 0.01
library(scales)
grid <- make.grid.under.curve(data$time, data$value, xpixel, ypixel)
ggplot(grid, aes(xmin = x, ymin = y, xmax = x+xpixel, ymax = y+ypixel, 
                 fill=abs(y))) + geom_rect() 

The colours aren't what you wanted, but it is probably too slow for serious use anyway.