trendanal.R

dfm <- data.frame(y = c(30, 43, 36, 33, 50, 45, 40) +
  scale(rnorm(7, 2, 5), scale = FALSE), x = 1:7)
dalt <- data.frame(x = seq(1, 7, length.out = 100))

m <- lapply(1:6, function(i) {lm(y ~ poly(x = x, degree = i), data = dfm)})

pdf(file = "tmp.pdf", height = 11, width = 8.5, onefile = TRUE)
par(mfrow = c(3, 2))
for(i in as.numeric(1:6)) {
  plot(y ~ x, data = dfm, main =
    substitute("Polynomial Trend Line: degree " == x, list(x = i)),
    pch = 16, cex = 1.2, ylim = range(dfm$y)*c(.9, 1.1))

  points(x = 1:7, y = predict(m[[i]], data.frame(x = 1:7)),
    type = "l", col = "plum4", lwd = 1.2)

  points(x = dalt$x, y = predict(m[[i]], dalt),
    type = "l", col = "lightslategrey", lwd = .2)

  text(x = 5, y = 35, labels =
    substitute(R^2 == x, list(x = round(summary(m[[i]])$r.squared, digits = 3))))
}
dev.off()