问如何将cobs样条软件包生成的数据显示为ggplot2

EN

library(cobs)

set.seed(1234)    # Make the results reproducible

x <- seq(-1, 3, , 150)
y <- (f.true <- pnorm(2*x)) + rnorm(150)/10
con <- rbind(c( 1,min(x),0), # f(min(x)) >= 0
             c(-1,max(x),1), # f(max(x)) <= 1
             c(0,  0,   0.5))# f(0)      = 0.5

wt1 <- cobs(x,y, constraint= "increase", lambda = 1, pointwise = con)

fit <- predict(wt1, x)[, 'fit']
df1 <- data.frame(x, y, fit)

ggplot(df1, aes(x, y)) +
  geom_point() +
  geom_line(aes(y = fit), colour = 'red')