如何使用斜率和截距來限制ggplot2中abline的長度？

Question

我如何使用斜率和截距將abline的長度限制在1985年至1990年之間。我知道geom_segment但它不需要斜率和攔截。 這裏是我的數據和腳本

> dput(df) 
structure(list(year = c(1979, 1980, 1981, 1982, 1983, 1984, 1985, 
1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 
1997, 1998), value = c(7.33, 10.32, 11.65, 6.19, 8.3, 9.24, 8.13, 
9.94, 10.85, 11.37, 7.17, 9.18, 11.24, 11.38, 8.32, 9.29, 7.48, 
8.63, 10.17, 8.94)), .Names = c("year", "value"), row.names = c(NA, 
-20L), class = c("tbl_df", "tbl", "data.frame")) 

腳本

plt <- ggplot(df, aes(year, value)) + 
    geom_line() + 
    geom_abline(aes(slope = 0.00225, intercept = 4.85100), colour = "red", lty = "dashed") 

plt 

Answer 1

只需使用geom_segment。計算給定x端點和斜率和截距的y端點是微不足道的。

xs = c(1985, 1990) 
beta = c(4.851, .00225) 
ys = cbind(1, xs) %*% beta 

... + 
geom_segment(aes(x = xs[1], xend = xs[2], y = ys[1], yend = ys[2]), 
    colour = "red",lty = "dashed")