Average line for 2D Histogram? - r

Question

I am a very new user of "R" and have a question.I am currently working on making 2D Histograms on R. The material necessarily does not matter but how do I plot an average line on the 2D Histogram. The code I am running is this:
load("mydatabin.RData")
# Color housekeeping
library(RColorBrewer)
rf <- colorRampPalette(rev(brewer.pal(11,'Spectral')))
r <- rf(32)
# Create normally distributed data for plotting
x <- mydata$AGE
y <- mydata$BP
df <- data.frame(x,y)
# Plot
plot(df, pch=16, col='black', cex=0.5)
This gives me a scatter plot and then to turn it into a 2D Histogram I do:
library(ggplot2)
# Default call (as object)
p <- ggplot(df, aes(x,y))
h3 <- p + stat_bin2d()
h3
# Default call (using qplot)
qplot(x,y,data=df, geom='bin2d')
After this I do:
h3 <- p + stat_bin2d(bins=25) + scale_fill_gradientn(colours=r)
h3
to add color.
Therefore, from here how do I plot an average line of the data.
And if anyone can tell me how to plot a heat map that looks like this using mydatebin.RData:
Thanks.

Answer 1

You can use geom_hline or geom_vline in ggplot2, passing y/xintercept as a parameter to draw a line. In your case, the parameter can be an average of one of your column to draw an average line. See the code for the example.
I also played around and tried two different ways to draw 2D histograms. Yours seems better and more precise, though I removed colorBrewer.
library(ggplot2)
# Create normally distributed data for plotting
x <- rnorm(10000)
y <- rnorm(10000)
df <- data.frame(x,y)
# stat_density2d way, with average lines
p1 <- ggplot(df,aes(x=x,y=y))+
stat_density2d(aes(fill=..level..), geom="polygon") +
scale_fill_gradient(low="navy", high="yellow") +
# Here go average lines
geom_hline(yintercept = mean(df$y), color = "red") +
geom_vline(xintercept = mean(df$x), color = "red") +
# Just to remove grid and set background color
theme(line = element_blank(),
panel.background = element_rect(fill = "navy"))
p1
# stat_bin2d way, with average lines
p2 <- ggplot(df, aes(x,y)) +
stat_bin2d(bins=50) +
scale_fill_gradient(low="navy", high="yellow") +
# Here go average lines
geom_hline(yintercept = mean(df$y), color = "red") +
geom_vline(xintercept = mean(df$x), color = "red") +
# Just to remove grid and set background color
theme(line = element_blank(),
panel.background = element_rect(fill = "navy"))
p2