R ggplot with two series: points and errorbars with legends - r

Question

If I have a dataframe like this:
obs<-rnorm(20)
d<-data.frame(year=2000:2019,obs=obs,pred=obs+rnorm(20,.1))
d$pup<-d$pred+.5
d$plow<-d$pred-.5
d$obs[20]<-NA
d
And I want the observation and model prediction error bars to look something like:
(p1<-ggplot(data=d)+aes(x=year)
+geom_point(aes(y=obs),color='red',shape=19)
+geom_point(aes(y=pred),color='blue',shape=3)
+geom_errorbar(aes(ymin=plow,ymax=pup))
)
How do I add a legend/scale/key identifying the red points as observations and the blue plusses with error bars as point predictions with ranges?

Answer 1

Here is one solution melting pred/obs into one column. Can't post image due to rep.
library(ggplot2)
obs <- rnorm(20)
d <- data.frame(dat=c(obs,obs+rnorm(20,.1)))
d$pup <- d$dat+.5
d$plow <- d$dat-.5
d$year <- rep(2000:2019,2)
d$lab <- c(rep("Obs", 20), rep("Pred", 20))
p1<-ggplot(data=d, aes(x=year)) +
geom_point(aes(y = dat, colour = factor(lab), shape = factor(lab))) +
geom_errorbar(data = d[21:40,], aes(ymin=plow,ymax=pup), colour = "blue") +
scale_shape_manual(name = "Legend Title", values=c(6,1)) +
scale_colour_manual(name = "Legend Title", values=c("red", "blue"))
p1
edit: Thanks for the rep. Image added

Answer 2

Here is a ggplot solution that does not require melting and grouping.
set.seed(1) # for reproducible example
obs <- rnorm(20)
d <- data.frame(year=2000:2019,obs,pred=obs+rnorm(20,.1))
d$obs[20]<-NA
library(ggplot2)
ggplot(d,aes(x=year))+
geom_point(aes(y=obs,color="obs",shape="obs"))+
geom_point(aes(y=pred,color="pred",shape="pred"))+
geom_errorbar(aes(ymin=pred-0.5,ymax=pred+0.5))+
scale_color_manual("Legend",values=c(obs="red",pred="blue"))+
scale_shape_manual("Legend",values=c(obs=19,pred=3))
This creates a color and shape scale wiith two components each ("obs" and "pred"). Then uses scale_*_manual(...) to set the values for those scales ("red","blue") for color, and (19,3) for scale.
Generally, if you have only two categories, like "obs" and "pred", then this is a reasonable way to go use ggplot, and avoids merging everything into one data frame. If you have more than two categories, or if they are integral to the dataset (e.g., actual categorical variables), then you are much better off doing this as in the other answer.
Note that your example left out the column year so your code does not run.