vertical alignment of gridExtra tableGrob (R grid graphics/grob) - r

Question

Having some trouble aligning a grid graphics object -- have read all the docs I can find, including the Murrell book, but no success. I think what I'm trying to do is pretty straightforward, so hopefully I'm missing simple.
Here's a reproducible example that will make a PDF of all the air carriers by destination in Hadley's hflights package (mirrors what I am trying to do on a different data set).
require(hflights)
require(gridExtra)
require(Cairo)
make_table <- function(df) {
p <- tableGrob(
df
,padding.h=unit(.25, "mm")
,show.rownames=FALSE
,gpar.coretext = gpar(fontsize=8, lineheight=0)
#this doesn't seem to justify the table
,just = c("bottom")
,show.box = T
)
return(p)
}
dests <- unique(hflights$Dest)
#list to hold the plots
plot_list <- list()
#loop over destinations and make a simple report
for (i in dests) {
#just this destination
this_dest <- hflights[hflights$Dest == i, ]
#the title
title <- textGrob(label = i, gp = gpar(fontsize=72, fontface = 'bold'))
#a table of carriers
carriers <- unique(this_dest$UniqueCarrier)
carriers <- data.frame(
carrier=carriers
)
carrier_table <- make_table(carriers)
#put them together
p <- arrangeGrob(
title, carrier_table
,nrow=2
)
plot_list[[i]] <- p
}
#print the report
Cairo(
width = 11, height = 8.5
,file = paste('destinations.pdf', sep = ''), type="pdf"
,units = "in"
)
print(plot_list)
dev.off()
I want the entire table produced by tableGrob (in the make_table function) to justify to the top of the grob. Right now it is centered vertically and horizontally inside the grob. Do I need to do that in the call to tableGrob, or is it in the arrangeGrob call? To ask it another way, in case the above is not clear, how can I make the whole table (not the text inside of it) justify to the top/bottom/left/right of its container?
Thanks!

Answer 1

try this,
library(gridExtra)
justify <- function(x, hjust="center", vjust="center", draw=TRUE){
w <- sum(x$widths)
h <- sum(x$heights)
xj <- switch(hjust,
center = 0.5,
left = 0.5*w,
right=unit(1,"npc") - 0.5*w)
yj <- switch(vjust,
center = 0.5,
bottom = 0.5*h,
top=unit(1,"npc") - 0.5*h)
x$vp <- viewport(x=xj, y=yj)
if(draw) grid.draw(x)
return(x)
}
g <- tableGrob(iris[1:3,1:2])
grid.newpage()
justify(g,"right", "top")