How can I show a polynomial of degree of different degree in ggplot2 with facet_grid?
I want to use edges (because I like the way they look for it) to show polynomial approaches of increasing degree. It's easy enough to break them apart separately like this:
df <- data.frame(x=rep(1:10,each=10),y=rnorm(100))
ggplot(df,aes(x=x,y=y)) + stat_smooth(method="lm",formula=y~poly(x,2))
ggplot(df,aes(x=x,y=y)) + stat_smooth(method="lm",formula=y~poly(x,3))
ggplot(df,aes(x=x,y=y)) + stat_smooth(method="lm",formula=y~poly(x,4))
I know I can always combine them using rodents, but I would like to combine them using facet_grid
if possible. Perhaps something similar to:
poly2 <- df
poly2$degree <- 2
poly3 <- df
poly3$degree <- 3
poly4 <- df
poly4$degree <- 4
polyn <- rbind(poly2,poly3,poly4)
ggplot(polyn,aes(x=x,y=y)) + stat_smooth(method="lm",formula=y~poly(x,degree)) +
facet_grid(degree~.)
This does not work, of course, because the cut does not work for y~poly(x,degree)
, therefore it degree
is extracted from the data. Is there a way to make this work?
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You can always predict points manually and then easily remove a face,
## Data
set.seed(0)
df <- data.frame(x=rep(1:10,each=10),y=rnorm(100))
## Get poly fits
dat <- do.call(rbind, lapply(1:4, function(d)
data.frame(x=(x=runif(1000,0,10)),
y=predict(lm(y ~ poly(x, d), data=df), newdata=data.frame(x=x)),
degree=d)))
ggplot(dat, aes(x, y)) +
geom_point(data=df, aes(x, y), alpha=0.3) +
geom_line(color="steelblue", lwd=1.1) +
facet_grid(~ degree)
To add confidence ranges, you can use the interval='confidence'
c option predict
. You may also be interested in a function ggplot2::fortify
to get more relevant statistics.
dat <- do.call(rbind, lapply(1:4, function(d) {
x <- seq(0, 10, len=100)
preds <- predict(lm(y ~ poly(x, d), data=df), newdata=data.frame(x=x), interval="confidence")
data.frame(cbind(preds, x=x, degree=d))
}))
ggplot(dat, aes(x, fit)) +
geom_point(data=df, aes(x, y), alpha=0.3) +
geom_line(color="steelblue", lwd=1.1) +
geom_ribbon(aes(x=x, ymin=lwr, ymax=upr), alpha=0.3) +
facet_grid(~ degree)
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I have a very ugly solution where the facet is faceted and the fits are plotted for the respective subsets of the data:
p1 <- ggplot(polyn,aes(x=x,y=y)) + facet_grid(.~degree)
p1 +
stat_smooth(data=polyn[polyn$degree==2,],formula=y~poly(x,2),method="lm") +
stat_smooth(data=polyn[polyn$degree==3,],formula=y~poly(x,3),method="lm") +
stat_smooth(data=polyn[polyn$degree==4,],formula=y~poly(x,4),method="lm")
gives
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