Multiple headers in facet_wrap (ggplot2)

Question

I am trying to add some headlines to the plot using facet_wrap and ggplot2. Say what you are, for example. have quarterly data for two years and want a graphical comparison of quarterly data with two main names; 2014 and 2015, as well as headings for the respective quarter.

I went so far:

data <- rnorm(10) A1 <- data.frame("Y"=data, "X"=1:10, "Q"=1, "year"=2014) A2 <- data.frame("Y"=data, "X"=1:10, "Q"=2, "year"=2014) A3 <- data.frame("Y"=data, "X"=1:10, "Q"=3, "year"=2014) A4 <- data.frame("Y"=data, "X"=1:10, "Q"=4, "year"=2014) N1 <- data.frame("Y"=data, "X"=1:10, "Q"=1, "year"=2015) N2 <- data.frame("Y"=data, "X"=1:10, "Q"=2, "year"=2015) N3 <- data.frame("Y"=data, "X"=1:10, "Q"=3, "year"=2015) N4 <- data.frame("Y"=data, "X"=1:10, "Q"=4, "year"=2015) A <- rbind(A1, A2, A3, A4) N <- rbind(N1, N2, N3, N4) tmp <- data.frame(rbind(A, N)) ggplot(data=tmp, aes(x=X, y=Y)) + geom_line() + facet_wrap(~year + Q, scales="free", ncol=4) 

which gives me this graph:

Instead, I would like “2014” and “2015” to be in two separate gray rectangles above each subgraph. Is it possible?

Thanks!

Answer 1

You beat me at RHA, I wrote an almost identical code to you before I saw your message. Anyway, thanks!

I also wanted to remove “2014” and “2015” from the gray boxes (which I did not indicate in my first post), so I had to make some additional changes.

With some inspiration from here , here , and here , I came up with the following (really ugly) code:

 data14 <- rnorm(10) data15 <- rnorm(10, mean = 500) A1 <- data.frame("Y"=data14, "X"=1:10, "Q"=1, "year"=2014) A2 <- data.frame("Y"=data14, "X"=1:10, "Q"=2, "year"=2014) A3 <- data.frame("Y"=data14, "X"=1:10, "Q"=3, "year"=2014) A4 <- data.frame("Y"=data14, "X"=1:10, "Q"=4, "year"=2014) N1 <- data.frame("Y"=data15, "X"=1:10, "Q"=1, "year"=2015) N2 <- data.frame("Y"=data15, "X"=1:10, "Q"=2, "year"=2015) N3 <- data.frame("Y"=data15, "X"=1:10, "Q"=3, "year"=2015) N4 <- data.frame("Y"=data15, "X"=1:10, "Q"=4, "year"=2015) A <- rbind(A1, A2, A3, A4) N <- rbind(N1, N2, N3, N4) tmp <- data.frame(rbind(A, N)) 

Then I made a simple function by naming the variables correctly

 labFunc <- function(data, var1, var2, names) { data$id <- NA loop <- length(levels(factor(data[[var2]]))) for (i in 1:loop) { data[data[[var1]] == 2014 & data[[var2]] == levels(factor(data[[var2]]))[i], "id"] <- names[i] data[data[[var1]] == 2015 & data[[var2]] == levels(factor(data[[var2]]))[i], "id"] <- paste(names[i], "") } first <- levels(factor(data$id))[seq(from=1, to = length(levels(factor(data$id))), by = 2)] second <- levels(factor(data$id))[seq(from=2, to = length(levels(factor(data$id))), by = 2)] data$id <- factor(data$id, levels=paste(c(first, second))) return(data) } names <- c("Q1", "Q2", "Q3", "Q4") data <- labFunc(tmp, "year", "Q", names) 

Make a plot:

 p <-ggplot(data, aes(y = Y, x = X)) + geom_line() + facet_wrap( ~ id , ncol = 4, scales = "free") 

And then finally add the main tags

 z <- ggplotGrob(p) # New strip at the top z <- gtable_add_rows(z, unit(1, "lines"), pos = 0) # New row added to top z <- gtable_add_rows(z, unit(1, "lines"), pos = 6) # New row added to top #z <- gtable_add_rows(z, unit(9, "lines"), pos = 0) # New row added to top # Check the layout gtable_show_layout(z) # New strip goes into row 2 # New strip spans columns 4 to 8 z <- gtable_add_grob(z, list(rectGrob(gp = gpar(col = NA, fill = grey(0.8), size = .5)), textGrob("2014", vjust = .27, gp = gpar(cex = .75, fontface = 'bold', col = "black"))), 2, 4, 2, 14, name = c("a", "b")) z <- gtable_add_grob(z, list(rectGrob(gp = gpar(col = NA, fill = grey(0.8), size = .5)), textGrob("2015", vjust = .27, gp = gpar(cex = .75, fontface = 'bold', col = "black"))), 7, 4, 7, 14, name = c("a", "b")) # Add small gap between strips - below row 2 z <- gtable_add_rows(z, unit(2/10, "lines"), 2) z <- gtable_add_rows(z, unit(5/10, "lines"), 7) # Draw it grid.newpage() grid.draw(z) 

It was a little harder than I thought, but thanks to everyone for their help!

Answer 2

Using the code here , as suggested by Sandy Muspratt, I can come up with:

 library(ggplot2) library(gtable) data <- rnorm(10) A1 <- data.frame("Y"=data, "X"=1:10, "Q"=1, "year"=2014) A2 <- data.frame("Y"=data, "X"=1:10, "Q"=2, "year"=2014) A3 <- data.frame("Y"=data, "X"=1:10, "Q"=3, "year"=2014) A4 <- data.frame("Y"=data, "X"=1:10, "Q"=4, "year"=2014) N1 <- data.frame("Y"=data, "X"=1:10, "Q"=1, "year"=2015) N2 <- data.frame("Y"=data, "X"=1:10, "Q"=2, "year"=2015) N3 <- data.frame("Y"=data, "X"=1:10, "Q"=3, "year"=2015) N4 <- data.frame("Y"=data, "X"=1:10, "Q"=4, "year"=2015) A <- rbind(A1, A2, A3, A4) N <- rbind(N1, N2, N3, N4) tmp <- data.frame(rbind(A, N)) p <- ggplot(data=tmp, aes(x=X, y=Y)) + geom_line() + facet_wrap(~year + Q, scales="free", ncol=4) z <- ggplotGrob(p) # New title strip at the top z <- gtable_add_rows(z, unit(1, "lines"), pos = 0) # New row added to top # Display the layout to select the place for the new strip gtable_show_layout(z) # New strip goes into row 2 # New strip spans columns 4 to 13 z <- gtable_add_grob(z, list(rectGrob(gp = gpar(col = NA, fill = grey(0.8), size = .5)), textGrob("2014", vjust = .27, gp = gpar(cex = .75, fontface = 'bold', col = "black"))), 2, 4, 2, 13, name = c("a", "b")) # Add small gap between strips - below row 2 z <- gtable_add_rows(z, unit(2/10, "line"), 2) # New title strip in the middle z <- gtable_add_rows(z, unit(1, "lines"), pos = 8) # New row added to top # Display the layout to select the place for the new strip gtable_show_layout(z) # New strip goes into row 9 # New strip spans columns 4 to 13 z <- gtable_add_grob(z, list(rectGrob(gp = gpar(col = NA, fill = grey(0.8), size = .5)), textGrob("2015", vjust = .27, gp = gpar(cex = .75, fontface = 'bold', col = "black"))), 9, 4, 9, 13, name = c("a", "b")) # Add small gap between strips - below row 2 z <- gtable_add_rows(z, unit(2/10, "line"), 9) # Draw it grid.newpage() grid.draw(z) 

What will this chart give you: