r - lines function returning too many random lines

Question

I have a weird problem with drawing a graph with confidence intervals for predictions.

Here is my code:

rm(list = ls())
cat("14")

set.seed(1)
file.name <- "testRegresji.pdf"
count = 20
pdf(file.name)

x <- runif(count, 0, 2)
y <- x + rnorm(count)
model <-lm(y ~ x)
xlab.label <- paste("y = ", format(model$coeff[1], digits = 4),
                    "+", format(model$coeff[2], digits = 4),
                    "* x + e")
plot(x, y, xlab = xlab.label, ylab = "", main = paste("n = ", count), col = 8)
matlines(x, predict(model, interval = "confidence"),
           type = 'l', lty = c(1, 2, 2), col = "black")
abline(0, 1, col = grey(0.4), lwd = 3)
  
dev.off()
shell.exec(paste(getwd(), "/", file.name, sep = ""))

The resulting graph looks very weird with too many random lines for confidence intervals, although the result of predict function are correct.

Here's the screenshot of the graph:

What could be the issue? Thanks a lot for any help!

question from:https://stackoverflow.com/questions/66053117/lines-function-returning-too-many-random-lines

Answer 1

Waitting for answers