facet_wrap text labelling issues with stat_fit_glance - r

Question

I am wondering why the text is trending higher in the plots... it won't stay put with the facet_wrap or facet_grid. In a more complex dataset plot, the text is illegible because of the overlap.
Below is data and code to reproduce the plot and issue. Adding geom="text" to stat_fit_glance, results in Error: Discrete value supplied to continuous scale .
library(ggpmisc)
library(ggplot2)
DF <- data.frame(Site = rep(LETTERS[20:24], each = 4),
Region = rep(LETTERS[14:18], each = 4),
time = rep(LETTERS[1:10], each = 10),
group = rep(LETTERS[1:4], each = 10),
value1 = runif(n = 1000, min = 10, max = 15),
value2 = runif(n = 1000, min = 100, max = 150))
DF$time <- as.numeric(DF$time)
formula1 <- y~x
plot1 <- ggplot(data=DF,
aes(x=time, y= value2,group=Site)) +
geom_point(col="gray", alpha=0.5) +
geom_line(aes(group=Site),col="gray", alpha=0.5) +
geom_smooth(se=F, col="darkorange", alpha=0.8, fill="orange",
method="lm",formula=formula1) +
theme_bw() +
theme(strip.text.x = element_text(size=10),
strip.text.y = element_text(size=10, face="bold", angle=0),
strip.background = element_rect(colour="black", fill="gray90"),
axis.text.x = element_text(size=10), # remove x-axis text
axis.text.y = element_text(size=10), # remove y-axis text
axis.ticks = element_blank(), # remove axis ticks
axis.title.x = element_text(size=18), # remove x-axis labels
axis.title.y = element_text(size=25), # remove y-axis labels
panel.background = element_blank(),
panel.grid.major = element_blank(), #remove major-grid labels
panel.grid.minor = element_blank(), #remove minor-grid labels
plot.background = element_blank()) +
labs(y="", x="Year", title = "")+ facet_wrap(~group)
plot1 + stat_fit_glance(method = "lm", label.x="right", label.y="bottom",
method.args = list(formula = formula1),
aes(label = sprintf('R^2~"="~%.3f~~italic(p)~"="~%.2f',
stat(..r.squared..),stat(..p.value..))),
parse = TRUE)

Answer 1

When the position of the labels is set automatically, the npcy position is increased for each level in the grouping variable. You map Site to the group aesthetic, as Site has 5 levels unevenly appearing in different facets, the rather crude algorithm in 'ggpmisc' positions the labels unevenly: the five rows correspond one to each of the five Sites. I have changed the mapping to use colour so that this becomes more obvious. I have also deleted all code that is irrelevant to this question.
plot1 <- ggplot(data=DF,
aes(x=time, y= value2, color=Site)) +
geom_smooth(se=F, alpha=0.8,
method="lm",formula=formula1) +
facet_wrap(~group)
plot1 +
stat_fit_glance(method = "lm", label.x="right", label.y="bottom",
method.args = list(formula = formula1),
aes(label = sprintf('R^2~"="~%.3f~~italic(p)~"="~%.2f',
stat(..r.squared..),stat(..p.value..))),
parse = TRUE) +
expand_limits(y = 110)
To use fixed positions one can pass the npcy coordinates if using the default "geom_text_npcy()" or passing data coordinates and using "geom_text()". One position corresponds to each level of the grouping factor Site. If the vector is shorter, it is recycled. Of course to fit more labels you can reduce the size of the text and add space by expanding the plotting area. In any case, in practice, you will need to indicate in a way or another which estimates correspond to which line.
plot1 +
stat_fit_glance(method = "lm", label.x="right", label.y= c(0.01, 0.06, 0.11, 0.01, 0.06),
method.args = list(formula = formula1),
aes(label = sprintf('R^2~"="~%.3f~~italic(p)~"="~%.2f',
stat(..r.squared..),stat(..p.value..))),
parse = TRUE, size = 2.5) +
expand_limits(y = 110)
Note: Error: Discrete value supplied to continuous scale when attempting to use
geom_text() is a bug in 'ggpmisc' that I fixed some days ago, but has not made it yet to CRAN (future version 0.3.3).