ggplot: colour of line segments according to variable value, like scale_color_gradient2

Question

I have a df "test_data", which contains values of the recent year ("recent"), the year before ("before") and the difference between these two ("delta").

in the given ggplot, the points are coloured according to the value of "delta" with scale_color_gradient2.

Line segments are drawn to link the points with the dashed line.

I was only able to colour all negative deltas in one colour (red) and all positive deltas in one colour (green), which does not reflect delta.

Is there a way to colour the line segments according to delta, like with scale_color_gradient2 for the points?

reproducable code:

library(ggplot2)
library(dplyr)

test_data<-structure(list(recent = c(65.2997185753145, 59.7196309660111,
                                     69.6283618162288, 72.8567667757411, 75.5042106908949, 65.9349599258225, 
                                     63.821946931775, 84.5492780693781, 70.1954593423904, 68.7330477506608, 
                                     74.7016955531504, 71.0329793728603, 90.8076584032142, 72.1556242719194),
                          before = c(68.1971224074475, 53.6815581922758, 67.3141074572482,
                                     70.8701488937935, 73.9713609414785, 63.2296191743796, 56.6943338152896, 
                                     81.7035240884654, 77.3175553964688, 69.7366705789213, 78.2019304405689, 
                                     71.6072916545225, 86.8455685297511, 75.7745946931338),
                          delta = c(-2.89740383213299, 6.03807277373529, 2.31425435898061, 
                                    1.98661788194759, 1.5328497494164, 2.7053407514429, 7.1276131164854, 
                                    2.8457539809127, -7.1220960540784, -1.0036228282605, -3.5002348874185, 
                                    -0.574312281662188, 3.96208987346309, -3.6189704212144)),
                     
                     row.names = c(NA,-14L),
                     class = "data.frame")
               
  
                                                                                                          

test_data<-test_data%>%
  mutate(x1_neg=case_when(delta<0 ~ before),
         y1_neg=case_when(delta<0 ~ recent),
         x2_neg=case_when(delta<0 ~ recent),
         y2_neg=case_when(delta<0 ~ recent))%>%
  mutate(x1_pos=case_when(delta>0 ~ before),
         y1_pos=case_when(delta>0 ~ recent),
         x2_pos=case_when(delta>0 ~ before),
         y2_pos=case_when(delta>0 ~ before))


plt<-ggplot(test_data, aes(x=before,y=recent))+
  geom_abline(slope=1,linetype = "dashed")+
  geom_segment(aes(x = x1_neg, y = y1_neg, xend = x2_neg, yend = y2_neg),
               colour="#E24C3B",
               size=1.3)+
  geom_segment(aes(x = x1_pos, y = y1_pos, xend = x2_pos, yend = y2_pos),
               colour="#ADCA1E",
               size=1.3)+
  geom_point(aes(color=delta),size=3)+
  scale_color_gradient2(high = "#ADCA1E",mid="#6ECFF6",low = "#E24C3B")+
  theme(plot.background = element_rect(fill = "#FFFFFF"),
        panel.background = element_rect(fill = "#FFFFFF"),
        axis.line = element_line(colour = "black"),
        panel.grid = element_line(colour = "#D2D0CF"),
        legend.justification = "bottom")+
  ylab("recent")+
  xlab("before")+
  coord_fixed()

x11(5,5)

plt

Answer 1

as @stefan mentioned, "delta" can be mapped on color in geom_segment. so if the plot definition is adapted like this, it works:

plt<-ggplot(test_data, aes(x=before,y=recent))+
  geom_abline(slope=1,linetype = "dashed")+
  geom_segment(aes(x = x1_neg, y = y1_neg, xend = x2_neg, yend = y2_neg, colour=delta),
               size=1.3)+
  geom_segment(aes(x = x1_pos, y = y1_pos, xend = x2_pos, yend = y2_pos, colour=delta),
               size=1.3)+
  geom_point(aes(color=delta),size=3)+
  scale_color_gradient2(high = "#ADCA1E",mid="#6ECFF6",low = "#E24C3B")+
  theme(plot.background = element_rect(fill = "#FFFFFF"),
        panel.background = element_rect(fill = "#FFFFFF"),
        axis.line = element_line(colour = "black"),
        panel.grid = element_line(colour = "#D2D0CF"),
        legend.justification = "bottom")+
  ylab("recent")+
  xlab("before")+
  coord_fixed()

x11(5,5)

plt