how to present the data with "<" in a PLOT - r

Question

I would like to plot a line + point plot. But my data contain "<" Is it possible to make the special point for the point with "<"? Any suggestion on how to better present those info?
Sample data:
df<-structure(list(Day = c(1, 3, 6, 7, 9, 12, 15), Score = c("0.1",
"0.5", "<1.3", "0.2", "<1.55", "0.8", "1.2")), row.names = c(NA,
-7L), class = c("tbl_df", "tbl", "data.frame"))
Here is my plot code and sample:
df<- df %>%
mutate(Score1=gsub("<", "", Score))
ggplot(data=df26, aes(x=Day,y=Score1, group=1)) +
geom_line()+
geom_point()

Answer 1

BTW, your Score1 is still in character type, so it is not plotting proportional to its value. Here's one approach to use the value without "<" but the label including the "<".
There are lots of options here. A few below:
add the "<" to the axis labels
add a visual indicator (could be color, text, an arrow, etc.) to note "smaller than" values.
Color differently and use a legend. I like ggtext for this as you can use markup to color in specific words, which is great for incorporating color legends into explanatory text.
Perhaps "<1.3" could be interpreted, based on situational knowledge, that the measurement was somewhere below 1.3 but not below 1.2. Then we could show simulated possibilities.
ggplot(data=df, aes(x=Day,y=as.numeric(Score1), group=1)) +
geom_line()+
geom_point() +
scale_y_continuous(breaks = as.numeric(df$Score1), labels = df$Score,
minor_breaks = NULL)
Or you might indicate visually that the values are smaller, esp. if there's some plausible range that they might be lower.
ggplot(data=df, aes(x=Day,y=as.numeric(Score1), group=1)) +
geom_line()+
geom_point() +
geom_segment(data = . %>% filter(Score1 != Score),
aes(xend = Day, yend = as.numeric(Score1) - 0.2),
arrow = arrow(length = unit(0.02, "npc")), color = "gray60") +
scale_y_continuous(breaks = as.numeric(df$Score1), labels = df$Score, minor_breaks = NULL)
library(ggtext)
ggplot(data=df, aes(x=Day, y=as.numeric(Score1), group = 1,
shape = Score1 == Score)) +
geom_line()+
geom_point(aes(color = Score1 == Score)) +
scale_shape_discrete(guide = FALSE) +
scale_color_manual(values = c("red", "black"), guide = FALSE) +
labs(caption = "<span style = 'color:#FF0000'>Red dots</span> were recorded with a '<'") +
theme(plot.caption = element_markdown())
Another idea is we might show possibilities that are consistent with the measurement based on our situational understanding of what "<1.3" means -- ie maybe it means the value was "somewhere between 1.2 and 1.3."
df_possibilities <- df %>%
filter(Score1 != Score) %>%
uncount(10) %>%
rowwise() %>%
mutate(adjusted = as.numeric(Score1) - runif(1, max = 0.1))
ggplot(data=df, aes(x=Day,y=as.numeric(Score1), group=1)) +
geom_line()+
geom_point() +
scale_y_continuous(breaks = as.numeric(df$Score1), labels = df$Score,
minor_breaks = NULL) +
geom_point(data = df_possibilities,
aes(y = adjusted), alpha = 0.1)

Answer 2

Couple of alternatives, inclulded in the same graph:
by a key using a coloured geom_point, or
by annotation with geom_text
This is just to give an impression, both methods can be enhanced and modified to provide the appearance you think provides the best visualisation.
library(ggplot2)
library(dplyr)
library(stringr)
df1 <-
df%>%
mutate(y = as.numeric(str_extract(Score, "\\d.\\d{1,2}")),
less_than = if_else(str_detect(Score, "<"), TRUE, FALSE))
ggplot(df1, aes(Day, y))+
geom_point(aes(colour = less_than))+
geom_line()+
geom_text(aes(label = Score), hjust = -0.2)
Created on 2021-04-15 by the reprex package (v2.0.0)

Answer 3

UPDATE
Labels idea from Peter. Thanks.
You can use shape for different shapes.
with ggpubr more sophisticated. Here a overview of the numbers:
ggplot(data=df, aes(x=factor(Day),y=Score1, group=1)) +
geom_line()+
geom_point() +
geom_point(data=df[c(3,5),], aes(x=factor(Day), y=Score1), colour="red", size=5, shape=25) +
geom_text(aes(label = Score), hjust = -0.2)+
theme_bw()