在ggplot2中添加水平线以绘制和图例 [英] Add a horizontal line to plot and legend in ggplot2

问题描述

此代码创建了一个不错的图，但我想在 y=50 处添加一条水平黑线，并让图例在图例中显示一条带有文本cutoff"的黑线，​​但在图例中为源保留点.我可以使用 geom_line 添加该行，但无法在图例中获取该行.

This code creates a nice plot but I would like to add a horizontal black line at y=50 AND have the legend show a black line with the text "cutoff" in the legend, but leave points in the legend for the sources. I can add the line with geom_line but cannot get the line in the legend.

    library(ggplot2)
    the.data <- read.table( header=TRUE, sep=",", 
    text="source,year,value
    S1,1976,56.98
    S1,1977,55.26
    S1,1978,68.83
    S1,1979,59.70
    S1,1980,57.58
    S1,1981,61.54
    S1,1982,48.65
    S1,1983,53.45
    S1,1984,45.95
    S1,1985,51.95
    S1,1986,51.85
    S1,1987,54.55
    S1,1988,51.61
    S1,1989,52.24
    S1,1990,49.28
    S1,1991,57.33
    S1,1992,51.28
    S1,1993,55.07
    S1,1994,50.88
    S2,1993,54.90
    S2,1994,51.20
    S2,1995,52.10
    S2,1996,51.40
    S3,2002,57.95
    S3,2003,47.95
    S3,2004,48.15
    S3,2005,37.80
    S3,2006,56.96
    S3,2007,48.91
    S3,2008,44.00
    S3,2009,45.35
    S3,2010,49.40
    S3,2011,51.19") 
    ggplot(the.data, aes( x = year, y = value ) ) + 
        geom_point(aes(colour = source)) + 
        geom_smooth(aes(group = 1))

推荐答案

(1) 试试这个:

cutoff <- data.frame( x = c(-Inf, Inf), y = 50, cutoff = factor(50) )
ggplot(the.data, aes( year, value ) ) + 
        geom_point(aes( colour = source )) + 
        geom_smooth(aes( group = 1 )) + 
        geom_line(aes( x, y, linetype = cutoff ), cutoff)

(2) 关于您的评论，如果您不希望将截止线列为单独的图例，则只需在图上标记截止线会更容易:

(2) Regarding your comment, if you don't want the cutoff listed as a separate legend it would be easier to just label the cutoff line right on the plot:

ggplot(the.data, aes( year, value ) ) + 
    geom_point(aes( colour = source )) + 
    geom_smooth(aes( group = 1 )) + 
    geom_hline(yintercept = 50) + 
    annotate("text", min(the.data$year), 50, vjust = -1, label = "Cutoff")

这看起来更好，并且可以推广到如图所示的多行:

This seems even better and generalizes to mulitple lines as shown:

line.data <- data.frame(yintercept = c(50, 60), Lines = c("lower", "upper"))
ggplot(the.data, aes( year, value ) ) + 
        geom_point(aes( colour = source )) + 
        geom_smooth(aes( group = 1 )) + 
        geom_hline(aes(yintercept = yintercept, linetype = Lines), line.data)

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