How to add total line on a ggplot stack bar chart - r

Question

I struggle to add a line on top with the total of this stacked barchart:
demandDriversdf = structure(list(year = structure(c(1356998400, 1388534400, 1420070400,
1451606400, 1483228800), tzone = "GMT", tclass = c("POSIXct",
"POSIXt"), class = c("POSIXct", "POSIXt")), one= c(12.4882571461364,
13.0984912135388, 12.1908055157534, 8.35335266490711, 4.38593754938248
), two= c(8.73113484771066, -4.34931681021004, -3.04955505552055,
-1.69136803847247, 3.06500464975644), three= c(0.0669199673877559,
-0.194488564805058, 0.721483847234409, 2.85829802643513, 6.14894193920574
), four= c(6.98748008979101, 3.7122726468811, -15.0029846301367,
-20.3768539034347, 9.38948700033012)), .Names = c("year", "one",
"two", "three", "four"), row.names = c("2013-01-01", "2014-01-01",
"2015-01-01", "2016-01-01", "2017-01-01"), class = "data.frame")
demandDriversdf2 = reshape2::melt(demandDriversdf, id.vars=c("year"), value.name="driver")
rowS = rowSums(demandDriversdf[,setdiff(colnames(demandDriversdf),"year")])
demandDriversdf2 = rbind(demandDriversdf2, data.frame(year = names(rowS), variable="Total", driver = rowS))
demandDriversdf2$year=substr(demandDriversdf2$year,1,4)
demandDriversdf2_1 <- subset(demandDriversdf2,driver >= 0 & variable!="Total")
demandDriversdf2_2 <- subset(demandDriversdf2,driver < 0 & variable!="Total")
gdemandDrivers = ggplot2::ggplot() +
ggplot2::geom_bar(data = demandDriversdf2_1, aes(x=year, y=driver, fill=variable),stat = "identity") +
ggplot2::geom_bar(data = demandDriversdf2_2, aes(x=year, y=driver, fill=variable),stat = "identity") +
ggplot2::geom_line(data = subset(demandDriversdf2, variable=="Total"), aes(x=year, y=driver)) +
ggplot2::scale_fill_brewer(palette = 2, type = "qual")
I get this strange warning
geom_path: Each group consists of only one observation. Do you need to
adjust the group aesthetic?
and ideally would like the line to be in black with also black points.

Answer 1

Just add group = 1 to aes() in geom_line():
library(ggplot2)
ggplot() +
geom_bar(data = demandDriversdf2_1, aes(x=year, y=driver, fill=variable),stat = "identity") +
geom_bar(data = demandDriversdf2_2, aes(x=year, y=driver, fill=variable),stat = "identity") +
geom_line(data = subset(demandDriversdf2, variable=="Total"),
aes(x=year, y=driver, group = 1)) +
scale_fill_brewer(palette = 2, type = "qual")
The reason for this:
For line graphs, the data points must be grouped so that it knows which points to connect. In this case, it is simple -- all points should be connected, so group=1. When more variables are used and multiple lines are drawn, the grouping for lines is usually done by variable.
Reference: Cookbook for R, Chapter: Graphs Bar_and_line_graphs_(ggplot2), Line graphs.