Displaying text below the plot generated by ggplot2

Question

I am trying to display some information about the data below the plot created in ggplot2. I would like to plot the N variable using the X axis coordinate of the plot but the Y coordinate needs to be 10% from the bottom of the screen . In fact, the desired Y coordinates are already in the data frame as y_pos variable.

I can think of 3 approaches using ggplot2:

1) Create an empty plot below the actual plot, use the same scale and then use geom_text to plot the data over the blank plot. This approach sort of works but is extremely complicated.

2) Use geom_text to plot the data but somehow use y coordinate as percent of the screen (10%). This would force the numbers to be displayed below the plot. I can't figure out the proper syntax.

3) Use grid.text to display the text. I can easily set it at the 10% from the bottom of the screen but I can't figure how set the X coordindate to match the plot. I tried to use grconvert to capture the initial X position but could not get that to work as well.

Below is the basic plot with the dummy data:

graphics.off()      # close graphics windows     library(car) library(ggplot2)  #load ggplot library(gridExtra) #load Grid library(RGraphics) # support of the "R graphics" book, on CRAN  #create dummy data test= data.frame(   Group = c("A", "B", "A","B", "A", "B"),    x = c(1 ,1,2,2,3,3 ),   y = c(33,25,27,36,43,25),   n=c(71,55,65,58,65,58),   y_pos=c(9,6,9,6,9,6)   )  #create ggplot p1 <- qplot(x, y, data=test, colour=Group) +   ylab("Mean change from baseline") +    geom_line()+   scale_x_continuous("Weeks", breaks=seq(-1,3, by = 1) ) +   opts(          legend.position=c(.1,0.9))  #display plot p1 

The modified gplot below displays numbers of subjects, however they are displayed WITHIN the plot. They force the Y scale to be extended. I would like to display these numbers BELOW the plot.

    p1 <- qplot(x, y, data=test, colour=Group) +   ylab("Mean change from baseline") +    geom_line()+   scale_x_continuous("Weeks", breaks=seq(-1,3, by = 1) ) +   opts( plot.margin = unit(c(0,2,2,1), "lines"),         legend.position=c(.1,0.9))+   geom_text(data = test,aes(x=x,y=y_pos,label=n))  p1 

A different approach of displaying the numbers involves creating a dummy plot below the actual plot. Here is the code:

graphics.off()      # close graphics windows     library(car) library(ggplot2)  #load ggplot library(gridExtra) #load Grid library(RGraphics) # support of the "R graphics" book, on CRAN  #create dummy data test= data.frame(   group = c("A", "B", "A","B", "A", "B"),    x = c(1 ,1,2,2,3,3 ),   y = c(33,25,27,36,43,25),   n=c(71,55,65,58,65,58),   y_pos=c(15,6,15,6,15,6)   )   p1 <- qplot(x, y, data=test, colour=group) +   ylab("Mean change from baseline") +    opts(plot.margin = unit(c(1,2,-1,1), "lines")) +   geom_line()+   scale_x_continuous("Weeks", breaks=seq(-1,3, by = 1) ) +   opts(legend.position="bottom",        legend.title=theme_blank(),        title.text="Line plot using GGPLOT")  p1  p2 <- qplot(x, y, data=test, geom="blank")+   ylab(" ")+   opts(     plot.margin = unit(c(0,2,-2,1), "lines"),             axis.line = theme_blank(),              axis.ticks = theme_segment(colour = "white"),                        axis.text.x=theme_text(angle=-90,colour="white"),             axis.text.y=theme_text(angle=-90,colour="white"),             panel.background = theme_rect(fill = "transparent",colour = NA),              panel.grid.minor = theme_blank(),                   panel.grid.major = theme_blank()             )+   geom_text(data = test,aes(x=x,y=y_pos,label=n))  p2  grid.arrange(p1, p2, heights = c(8.5, 1.5),             nrow=2 ) 

However, that is very complicated and would be hard to modify for different data. Ideally, I'd like to be able to pass Y coordinates as percent of the screen.

Answer 1

The current version (>2.1) has a + labs(caption = "text"), which displays an annotation below the plot. This is themeable (font properties,... left/right aligned). See https://github.com/hadley/ggplot2/pull/1582 for examples.

Answer 2

Edited opts has been deprecated, replaced by theme; element_blank has replaced theme_blank; and ggtitle() is used in place of opts(title = ...

Sandy- thank you so much!!!! This does exactly what I want. I do wish we could control the clipping in geom.text or geom.annotate.

I put together the following program if anybody else is interested.

 rm(list = ls())     # clear objects    graphics.off()      # close graphics windows     library(ggplot2) library(gridExtra)  #create dummy data test= data.frame(   group = c("Group 1", "Group 1", "Group 1","Group 2", "Group 2", "Group 2"),    x = c(1 ,2,3,1,2,3 ),   y = c(33,25,27,36,23,25),   n=c(71,55,65,58,65,58),   ypos=c(18,18,18,17,17,17)    )   p1 <- qplot(x=x, y=y, data=test, colour=group) +   ylab("Mean change from baseline") +    theme(plot.margin = unit(c(1,3,8,1), "lines")) +   geom_line()+   scale_x_continuous("Visits", breaks=seq(-1,3) ) +   theme(legend.position="bottom",        legend.title=element_blank())+    ggtitle("Line plot")    # Create the textGrobs  for (ii in 1:nrow(test)) {   #display numbers at each visit   p1=p1+ annotation_custom(grob = textGrob(test$n[ii]),                              xmin = test$x[ii],                             xmax = test$x[ii],                             ymin = test$ypos[ii],                             ymax = test$ypos[ii])      #display group text     if (ii %in% c(1,4)) #there is probably a better way        {     p1=p1+ annotation_custom(grob = textGrob(test$group[ii]),                                xmin = 0.85,                               xmax = 0.85,                               ymin = test$ypos[ii],                               ymax = test$ypos[ii])     }    }       # Code to override clipping   gt <- ggplot_gtable(ggplot_build(p1))   gt$layout$clip[gt$layout$name=="panel"] <- "off"   grid.draw(gt)