Inconsistent default directions in scale_fill_brewer() and scale_fill_distiller()

[UweBlock]

The new introduced direction parameter (#1139) has different default values as can be seen in the help file. For brewer the default direction is +1, for distiller the default direction is -1 which is breaking existing codes.
Is there a specific reason for this?
Thanks & brgds,
Uwe

From the Usage section of the help file:

scale_colour_brewer(..., type = "seq", palette = 1, direction = 1)
scale_fill_brewer(..., type = "seq", palette = 1, direction = 1)
scale_colour_distiller(..., type = "seq", palette = 1, direction = -1,
  values = NULL, space = "Lab", na.value = "grey50",
  guide = "colourbar")
scale_fill_distiller(..., type = "seq", palette = 1, direction = -1,
  values = NULL, space = "Lab", na.value = "grey50",
  guide = "colourbar")

[hadley]

@jiho was this deliberate?

[jiho]

It was, the reason for it is:

1. for sequential scales, darker tones are associated with high values.
2. for diverging scales, the default direction of the brewer scales associates cold colours with high values and conversely.

The best choice for 1 is debatable but the default continuous color scale in ggplot2 goes from dark to light, so at least those are consistent. 2 was clearly "wrong".

Another possibility would be to default to 1 and reverse the colours internally, but I wanted to make it obvious that the setting was different for scale_*_brewer and scale_*_distiller. If it was just me, I would actually reverse the colours for scale_*_brewer too and make this the default.

Examples

library("ggplot2")
library("reshape2")
library("RColorBrewer")
d <- melt(volcano, varnames=c("x", "y"), value.name="z")

# default
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster()
# current default
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_distiller(palette="Blues")
# "regular" direction (given by RColorBrewer)
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_distiller(palette="Blues", direction=1)
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_gradientn(colors=brewer.pal(name="Blues", n=6))

# and with a diverging scale
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_distiller(palette="Spectral")

ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_distiller(palette="Spectral", direction=1)
ggplot(d, aes(x=x, y=y, fill=z)) + geom_raster() + scale_fill_gradientn(colors=brewer.pal(name="Spectral", n=6))