R ggplot2 Multiple Lines in Connected Scatterplot

Question

I need to plot multiple lines in a connected scatterplot, but am running into issues. I can plot one line, but not the other (or more).

Code

library(dplyr)
library(ggplot2)
library(ggrepel)
library(tidyr)

year<-c(2010,2011,2012,2013,2014,2015,2016,2017,2018,2019)

variableA1<-c(56,169,313,595,797,989,934,869,824,662)
variableB1<-c(0,0,5,12,23,44,73,71,78,103)

variableA2<-c(22,58,159,342,603,1021,1589,2071,2268,2044)
variableB2<-c(1,1,0,3,7,9,33,59,84,98)


data<-data.frame(year,variableA1,variableB1,variableA2,variableB2)

data %>% 
  ggplot(aes(x=variableA1, y=variableB1, label=year)) +
     geom_point(color="#333333") + 
     geom_text_repel() +
     geom_segment(color="#333333", 
                aes(
                    xend=c(tail(variableA1, n=-1), NA), 
                    yend=c(tail(variableB1, n=-1), NA)
                ),
                arrow=arrow(length=unit(0.3,"cm"))
                ) +
     geom_point(color="#a8a8a8") + 
     geom_text_repel() +
     geom_segment(color="#a8a8a8", 
                aes(
                    xend=c(tail(variableA2, n=-1), NA), 
                    yend=c(tail(variableB2, n=-1), NA)
                ),
                arrow=arrow(length=unit(0.3,"cm"))
                )

ggplot Chart

Connected Scatterplot

mrhd · Accepted Answer · 2020-05-15 16:17:33Z

1

This is not really the way to do things with ggplot2.

Instead, you define the x and y coordinates for both series in the same columns and add another column that specifies which data series the values belong to.

EDIT

The segment coordinates (for the arrows) should also be set explicitly for each data series:

data_points<-data.frame(year = year, varA = variableA1, varB = variableB1, series = "series1") %>%
  bind_rows(data.frame(year = year, varA = variableA2, varB = variableB2, series = "series2"))

data_lines<-data.frame(
    x = head(variableA1, n=-1),
    y = head(variableB1, n=-1),
    xend = tail(variableA1, n=-1),
    yend = tail(variableB1, n=-1),
    series = "series1") %>%
  bind_rows(
    data.frame(
      x = head(variableA2, n=-1), 
      y = head(variableB2, n=-1), 
      xend = tail(variableA2, n=-1),
      yend = tail(variableB2, n=-1), 
      series = "series2")
  )

data_points %>% 
  ggplot(aes(x=varA, y=varB, label=year, color=series)) +
  geom_point(color="#333333") + 
  geom_text_repel() +
  geom_segment(data = data_lines,
               aes(x = x, y = y, xend = xend, yend = yend, 
                   color = series, label=NA),
               arrow=arrow(length=unit(0.3,"cm"))
  ) +
  scale_color_manual( values = c('#333333', '#a8a8a8'))

edited May 15, 2020 at 16:17

answered May 15, 2020 at 13:44

mrhd

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3 Comments

Rahul Over a year ago

Thanks. That seems closer to what I was looking for, but how do I avoid that this is one continuous graph? In the figure above, 2019 in the first series is connected to 2010 of the second series. I need them to be two "separate" lines.

mrhd Over a year ago

You're righ @Rahul, the start and end coordinates of the line segments are still off. They need to be specified differently. I'll have a look a bit later.

mrhd Over a year ago

Have a look now. I edited the answer to include the correct coordinates for the arrow segments.

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