How can I draw diamonds in R with ggplot2? - r

Question

I am trying to replicate the following picture in R, in particular with ggplot2
I was able to draw the red rss contour lines but I've no idea how to draw a diamond (like the one in the left picture). The "expected Output" should be a way to draw a diamond with a given side length.
EDIT: Here is a short reproducible example to add the diamond randomly inside the following plot:
mlb<- read.table('https://umich.instructure.com/files/330381/download?download_frd=1', as.is=T, header=T)
str(mlb)
fit<-lm(Height~Weight+Age-1, data = as.data.frame(scale(mlb[,4:6])))
points = data.frame(x=c(0,fit$coefficients[1]),y=c(0,fit$coefficients[2]),z=c("(0,0)","OLS Coef"))
Y=scale(mlb$Height)
X = scale(mlb[,c(5,6)])
beta1=seq(-0.556, 1.556, length.out = 100)
beta2=seq(-0.661, 0.3386, length.out = 100)
df <- expand.grid(beta1 = beta1, beta2 = beta2)
b = as.matrix(df)
df$sse <- rep(t(Y)%*%Y,100*100) - 2*b%*%t(X)%*%Y + diag(b%*%t(X)%*%X%*%t(b))
base <- ggplot() +
stat_contour(data=df, aes(beta1, beta2, z = sse),breaks = round(quantile(df$sse, seq(0, 0.2, 0.03)), 0),
size = 0.5,color="darkorchid2",alpha=0.8) +
scale_x_continuous(limits = c(-0.4,1))+
scale_y_continuous(limits = c(-0.55,0.4))+
geom_point(data = points,aes(x,y))+
geom_text(data = points,aes(x,y,label=z),vjust = 2,size=3.5)
base

Answer 1

You can draw shapes with geom_polygon.
library(ggplot2)
df <- data.frame(x = c(1, 0, -1, 0), y = c(0, 1, 0, -1))
ggplot(df) + geom_polygon(aes(x = x, y = y))
If you want to generate the coordinates from a center and a side length, you can transform a base matrix. You can also combine this with an existing plot by supplying the coordinates to the data argument of the geom instead of to ggplot() as shown. Change the sqrt2 scaling if you want the corner-to-center as the argument instead of the side length.
diamond <- function(side_length, center) {
base <- matrix(c(1, 0, 0, 1, -1, 0, 0, -1), nrow = 2) * sqrt(2) / 2
trans <- (base * side_length) + center
as.data.frame(t(trans))
}
ggplot() + geom_polygon(data = diamond(2, c(1, 2)), mapping = aes(x = V1, y = V2))
Here's an example of adding it in to your provided data. Note that I put it before (underneath) the text, and named the arguments to be clear (probably the source of that object coercible by fortify error.
mlb <- read.table("https://umich.instructure.com/files/330381/download?download_frd=1", as.is = T, header = T)
fit <- lm(Height ~ Weight + Age - 1, data = as.data.frame(scale(mlb[, 4:6])))
points <- data.frame(x = c(0, fit$coefficients[1]), y = c(0, fit$coefficients[2]), z = c("(0,0)", "OLS Coef"))
Y <- scale(mlb$Height)
X <- scale(mlb[, c(5, 6)])
beta1 <- seq(-0.556, 1.556, length.out = 100)
beta2 <- seq(-0.661, 0.3386, length.out = 100)
df <- expand.grid(beta1 = beta1, beta2 = beta2)
b <- as.matrix(df)
df$sse <- rep(t(Y) %*% Y, 100 * 100) - 2 * b %*% t(X) %*% Y + diag(b %*% t(X) %*% X %*% t(b))
ggplot(df) +
stat_contour(aes(beta1, beta2, z = sse),
breaks = round(quantile(df$sse, seq(0, 0.2, 0.03)), 0),
size = 0.5, color = "darkorchid2", alpha = 0.8
) +
geom_polygon(data = diamond(0.1, c(0, 0)), mapping = aes(x = V1, y = V2), fill = "cadetblue1") +
scale_x_continuous(limits = c(-0.4, 1)) +
scale_y_continuous(limits = c(-0.55, 0.4)) +
geom_point(data = points, aes(x, y)) +
geom_text(data = points, aes(x, y, label = z), vjust = 2, size = 3.5)
#> Warning: Removed 4215 rows containing non-finite values (stat_contour).
Created on 2018-08-01 by the reprex package (v0.2.0).