[R] How to alpha entire plot?

[Boris Steipe]

Interesting problem.

I would discretize the x-values and interleave them. Lines from one dataset still overlap, so you see high- density and low-density regions, but lines from the other dataset are drawn into the interval. Like so:

interleave <- function(x, MIN, MAX, N, nChannel = 2, channel) {
  
  isp <- seq(MIN, MAX, length.out = N + 1) # interleave support points
  offset <- ((isp[2] - isp[1]) / nChannel) * (channel - 1) # offset for channel
  
  # round x to the nearest support point and add the channel specific offset
  x <- isp[round(as.numeric(cut(x, breaks = N)))] + offset
  
  return(x)
}

xi <- min(EU$DAX)
xa <- max(EU$DAX)

plot(interleave(EU$DAX, MIN=xi, MAX=xa, N=130, channel=1 ),
     EU$CAC,
     col = "#6600EE07",
     type = "h",
     ylim = c(0,6000),
     xlab = "DAX")

points(interleave(EU$DAX, MIN = xi, MAX = xa, N = 130, channel = 2 ),
     EU$FTSE,
     col = "#EE000007",
     type = "h")


Cheers,
B.



> On 2018-05-31, at 16:56, Ed Siefker <ebs15242 using gmail.com> wrote:
> 
> I have two chromatograms I want plotted on the same axes.
> I would like the plots to be transparent, so the first chart is
> not obscured.
> 
> I have tried adjustcolor(..., alpha.f=0.3), the problem is that
> my chromatogram is so dense with datapoints that they
> overlap and the entire graph just ends up a solid color.  The
> second histogram still obscures the first.
> 
> Consider this example:
> 
> 
> col1 <- adjustcolor("red", alpha.f=0.3)
> col2 <- adjustcolor("blue", alpha.f=0.3)
> EU <- data.frame(EuStockMarkets)
> with(EU, plot(DAX, CAC, col=col2, type="h", ylim=c(0,6000)))
> par(new=TRUE)
> with(EU, plot(DAX, FTSE, col=col1, type="h", ylim=c(0,6000)))
> 
> The density of the red plot around 2000 completely obscures the blue
> plot behind it.
> 
> What I would like to do is plot both plots in solid colors, then alpha
> the entire thing, and then overlay them.  Or some other method that
> achieves a comparable result.
> Thanks
> 
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