[R] Lines in a line graph not visible when values are identical

[Bob Green]

Hello,

I'm pretty rusty using R but wanted to compare 
four parameters measured in mm, in terms of the year an object was created.

My problem is that where there are identical 
values, only one line is produced. For example, 
for the first parameter "tail",only five of a possible eight lines are visible.

The code and full dataset are below. I considered 
making trivial differences to identical values of 
a parameter to create difference,but no doubt 
there are more elegant or sophisticated options.

Any advice is appreciated,

Bob

library(ggplot2)
library(tidyr)
library(readxl)
DF <- read_excel("C:/Files/DataLong.xlsx")
DF


DF$Parameter <- factor(DF$Parameter, levels = 
c("Tail", "Tail_b", "Noseb", "Nose"))


ggplot(DF, aes(x = Parameter, y = Millimetres, color = Year, group = Year)) +
   geom_line(linewidth = 1) +
   geom_point(size = 2) + labs(title = 
"Parameters by Year", x = "Parameter", y = "Millimetres ($)") +
   theme_minimal()

##Data


# A tibble: 32 × 3
    Parameter Millimetres Year
    <fct>           <dbl> <chr>
  1 Tail             0    2010-2012
  2 Tail_b           0    2010-2012
  3 Nose_b          20.3  2010-2012
  4 Nose            74.9  2010-2012
  5 Tail             0    2014
  6 Tail_b           0    2014
  7 Nose_b          14    2014
  8 Nose            63.7  2014
  9 Tail            11.2  2016
10 Tail_b           2.8  2016
11 Nose_b          16.3  2016
12 Nose            72.6  2016
13 Tail             0    2023
14 Tail_b           0    2023
15 Nose_b          17.1  2023
16 Nose            72.5  2023
17 Tail            11.3  2024
18 Tail_b           2.9  2024
19 Nose_b          16.9  2024
20 Nose            74.7  2024
21 Tail            28.1  2025C
22 Tail_b           4.9  2025C
23 Nose_b           6.8  2025C
24 Nose            37.7  2025C
25 Tail            25.9  2025B
26 Tail_b           5.2  2025B
27 Nose_b          11.2  2025B
28 Nose            68.1  2025B
29 Tail            30.2  2026
30 Tail_b           6.35 2026
31 Nose_b          15.1  2026
32 Nose            76.2  2026