How to place grobs with annotation_custom() at precise areas of the plot region?
Here's how I would approach this,
library(gtable)
library(ggplot2)
library(plyr)
set.seed(1)
d <- data.frame(x=rep(1:10, 5),
y=rnorm(50),
g = gl(5,10))
# example plot
p <- ggplot(d, aes(x,y,colour=g)) +
geom_line() +
scale_x_continuous(expand=c(0,0))+
theme(legend.position="top",
plot.margin=unit(c(1,0,0,0),"line"))
# dummy data for the legend plot
# built with the same y axis (same limits, same expand factor)
d2 <- ddply(d, "g", summarise, x=0, y=y[length(y)])
d2$lab <- paste0("line #", seq_len(nrow(d2)))
plegend <- ggplot(d, aes(x,y, colour=g)) +
geom_blank() +
geom_segment(data=d2, aes(x=2, xend=0, y=y, yend=y),
arrow=arrow(length=unit(2,"mm"), type="closed")) +
geom_text(data=d2, aes(x=2.5,label=lab), hjust=0) +
scale_x_continuous(expand=c(0,0)) +
guides(colour="none")+
theme_minimal() + theme(line=element_blank(),
text=element_blank(),
panel.background=element_rect(fill="grey95", linetype=2))
# extract the panel only, we don't need the rest
gl <- gtable_filter(ggplotGrob(plegend), "panel")
# add a cell next to the main plot panel, and insert gl there
g <- ggplotGrob(p)
index <- subset(g$layout, name == "panel")
g <- gtable_add_cols(g, unit(1, "strwidth", "line # 1") + unit(1, "cm"))
g <- gtable_add_grob(g, gl, t = index$t, l=ncol(g),
b=index$b, r=ncol(g))
grid.newpage()
grid.draw(g)
It should be straight-forward to adapt the "legend" plot with specific tags and locations (left as an exercise for the interested reader).
Maybe this can illustrate annotation_custom
,
myGrob <- grobTree(rectGrob(gp=gpar(fill="red", alpha=0.5)),
segmentsGrob(x0=0, x1=1, y0=0, y1=1, default.units="npc"))
myGrob2 <- grobTree(rectGrob(gp=gpar(fill="blue", alpha=0.5)),
segmentsGrob(x0=0, x1=1, y0=0, y1=1, default.units="npc"))
p <- qplot(1:10, 1:10) + theme(plot.margin=unit(c(0, 3, 0, 0), "cm")) +
annotation_custom(myGrob, xmin=5, xmax=6, ymin=3.5, ymax=5.5) +
annotate("segment", x=5, xend=6, y=3, yend=5, colour="red") +
annotation_custom(myGrob2, xmin=8, xmax=12, ymin=3.5, ymax=5.5)
p
g <- ggplotGrob(p)
g$layout$clip[g$layout$name=="panel"] <- "off"
grid.draw(g)
There's a weird bug apparently, whereby if I reuse myGrob
instead of myGrob2
, it ignores the placement coordinates the second time and stacks it up with the first layer. This function is really buggy.