Getting used to the grammar of ggplot2 takes some time, but so far it's not been disappointing. Wanting to split a scatterplot by segment, I used
facet_grid. That by default shows a label on each subplot, using the values in the variable by which the plot is faceted.
As that often isn't very descriptive in itself, there needs to be a way to re-label these subplots. That way is
as_labeller, as shown in the example code below.
ggplot(outputs, aes(x=date_var,y=value_var),alpha=0.8) + geom_point(aes(y=value_var, colour=colour_var)) + geom_smooth() + theme(legend.position = "none",axis.text.y = element_blank(),axis.text.x = element_blank()) + scale_x_date(date_breaks = '1 week') + labs(y = "Value",x = "Date", title = "Example") + scale_colour_manual("Legend",values=named_coloring_vector)) + scale_fill_manual("",values=c("grey12")) + facet_grid(. ~ Segment, labeller = as_labeller(c("yes" = "Segment A", "no" = "Segment B")))