ggplot2 geom_line()应指向指定值 [英] ggplot2 geom_line() should point at specified value

问题描述

我写了以下代码:

library(ggplot2)

data <- structure(list(x = c(1L, 6L, 3L, 4L, 2L, 3L, 6L, 1L, 5L, 2L, 
                    1L, 5L), y = c(1L, 7L, 5L, 6L, 3L, 4L, 6L, 2L, 5L, 6L, 5L, 2L
            ), year = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 
                            2L, 2L), .Label = c("2010", "2011"), class = "factor"), matching = structure(c(1L, 
                            2L, 3L, 4L, 5L, 6L, 1L, 2L, 3L, 4L, 5L, 6L), .Label = c("person1", 
                            "person2", "person3", "person4", "person5", "person6"), class = "factor")), .Names = c("x", 
            "y", "year", "matching"), row.names = c(NA, -12L), class = "data.frame")

data$year <- factor(data$year)

colors <- c("#4cb5ee", "#a0d099", "red")

p <- ggplot(data, aes(x=x, y=y)) +
    geom_point(aes(colour=year), shape=16, size=6) +
    geom_line(aes(group=matching), arrow=arrow(length=unit(0.15,"cm")), colour="black", size=1) +
    xlab("x") + ylab("y") +
    scale_colour_manual("year", values=colors) +
    scale_x_continuous(limits=c(1,7), breaks=seq(1,7, by=1)) +
    scale_y_continuous(limits=c(1,7), breaks=seq(1,7, by=1))

print(p)

它给出以下输出:

但是我想要geom_line()做的是:总是指向year = 2011的点.我无法弄清楚为什么有时箭头指向的点是是指year = 2010，有时是指向year = 2011的点.

But what I want geom_line() to do is: always points at the point where year=2011. I can't figure out why the arrow of the line is point sometimes at a point which refers to year=2010 and sometimes points at a point where year=2011.

我发现箭头包含几个参数:

What I found out is that arrow takes several arguments:

arrow(angle = 30, length = unit(0.25, "inches"), ends = "last", type = "open") 

这样我可以说ends="first".但是我不能一概而论ends总是first还是总是last.

So that I could say ends="first". But I can't generalize that ends is always first or always last.

我试图在data.frame中添加一列，该列包含有关箭头应该是第一个还是最后一个结束的信息，但是并没有提供我想要的输出.

I tried to add a column to my data.frame which has the information if the arrow should end first or last, but it didn't gives me the output I wanted.

我们非常感谢您的帮助:-)

Every help is highly appreciated :-)

提前谢谢！

推荐答案

geom_path应该可以解决问题:

p <- ggplot(data, aes(x=x, y=y)) +
    geom_point(aes(colour=year), shape=16, size=6) +
    geom_path(aes(group=matching), 
                  arrow=arrow(length=unit(0.15,"cm")),
                  colour="black", size=1) +
    xlab("x") + ylab("y") +
    scale_colour_manual("year", values=colors) +
    scale_x_continuous(limits=c(1,7), breaks=seq(1,7, by=1)) +
    scale_y_continuous(limits=c(1,7), breaks=seq(1,7, by=1))

print(p)

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