[R] How to plot both lines and points by group on ggplot2

[Chris Evans]

[Whoops, forgot that default reply-to is to the sender.]


On 01/07/2023 19:20, Luigi Marongiu wrote:
> Hello,
> I have a dataframe with measurements stratified by the concentration
> of a certain substance. I would like to plot the points of the
> measures and connect the points within each series of concentrations.
> When I launch ggplot2 I get the error
> ```
> geom_path: Each group consists of only one observation. Do you need to
> adjust the
> group aesthetic?
> ```
> and no lines are drawn.
> Where am I going wrong?
> Thank you
> Luigi
>
> ```
> df = data.frame(Conc = c(rep(1, 3), rep(2, 3), rep(5, 3)),
> Time = rep(1:3, 3),
> Value = c(0.91, 0.67, 0.71, 0.91, 0.65, 0.74, 0.95, 0.67, 0.67))
> df$Time <- as.factor(df$Time)
> levels(df$Time) = c(1, 4, 24)
> df$Conc <- as.factor(df$Conc)
> levels(df$Conc) = c(1, 2, 5)
> library(ggplot2)
> ggplot(df, aes(x=Time, y=Value, colour=Conc)) +
> geom_point(size=6) +
> geom_line(aes(x=Time, y=Value, colour=Conc)) +
> scale_colour_manual(values = c("darkslategray3", "darkslategray4",
> "deepskyblue4")) +
> ggtitle("Working example") +
> xlab(expression(bold("Time (h)"))) +
> ylab(expression(bold("Concentration (mM)")))
> ```

If I understand what you want then I think all you need is to add "group 
= Conc".  That's what that message is telling you.

df = data.frame(Conc = c(rep(1, 3), rep(2, 3), rep(5, 3)),
                 Time = rep(1:3, 3),
                 Value = c(0.91, 0.67, 0.71, 0.91, 0.65, 0.74, 0.95, 
0.67, 0.67))
df$Time <- as.factor(df$Time)
levels(df$Time) = c(1, 4, 24)
df$Conc <- as.factor(df$Conc)
levels(df$Conc) = c(1, 2, 5)
library(ggplot2)
ggplot(df, aes(x=Time, y=Value, colour=Conc, group = Conc)) +
   geom_point(size=6) +
   geom_line(aes(x=Time, y=Value, colour=Conc)) +
   scale_colour_manual(values = c("darkslategray3", "darkslategray4",
                                  "deepskyblue4")) +
   ggtitle("Working example") +
   xlab(expression(bold("Time (h)"))) +
   ylab(expression(bold("Concentration (mM)")))

Very  best,


Chris

-- 
Chris Evans (he/him)
Visiting Professor, UDLA, Quito, Ecuador & Honorary Professor, University of Roehampton, London, UK.
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