R Question

Add a customized x-axis to plot ggplot2 and y-axis as well

I have the following code:

df=data.frame(time=as.factor(rep(0.5:9.5,each=10)),
roi=rep(1:10,10),
area=runif(100, 5.0, 7.5))

df$time=factor(df$time, levels=rev(levels(df$time)))

ggplot(data=df, aes(x=factor(roi), y=time, fill = area)) +
theme_minimal() + coord_fixed(ratio=1) +
geom_tile(colour = NA, width = 1.5, height = 1) +
scale_fill_gradient(low="black",high="white")


Now, I want to remove the x-axis and add a new one to have the expected fig below. The x-axis will be divided into 4 parts for 4 segs with 39%,23%,23%,15% of axis length for Seg 1, Seg 2, Seg 3, Seg 4, respectively. Could anybody hava any idea to solve it. I apprecicate all response and am looking forward your answers.

Great thanks to Mark Heckmann for helpful answer to my problem. I would like to ask one more thing. I also want to modify the y-axis by "scale_y_discrete", the code ran well but the y-axis label did not meet my expectation. The code I ran is:

ggplot(data=df, aes(x=factor(roi), y=time, fill = area)) + theme_minimal() +coord_fixed(ratio=1) +geom_tile(colour = NA, width = 1.5, height = 1)+scale_fill_gradient(low="black",high="white") +scale_y_discrete(name="Time (min)",expand =c(0.01,0.1),breaks=c(1,2.5,5.0,7.5,10.0),labels=c(0,15,30,45,60))


Thank you very much!

enter image description here

Answer

You need to use annotation_custom to draw outside the plotting area.

#### your plot

g <- ggplot(data=df, aes(x=factor(roi), y=time, fill = area)) + 
  theme_minimal() + coord_fixed(ratio=1) +
  geom_tile(colour = NA, width = 1.5, height = 1) + 
  scale_fill_gradient(low="black",high="white") 

Extra code:

# remove axis 
g <- g +  theme(axis.title.x=element_blank(),
             axis.text.x=element_blank(),
              axis.ticks.x=element_blank()) +
          scale_x_discrete(expand = c(0,0)) 

# calculate segment coordinates
segs <- c(.39, .23, .23, .15)
segs_center <- cumsum(segs) - segs/2
seg_ticks <- cumsum(segs)[1:3]
seg_labels <- paste("Seg", seq_along(segs))

# create graphicaal objects and gather as tree
grobs <- grobTree(linesGrob(c(0,1), c(.5,.5)),
                  segmentsGrob(x0=seg_ticks, x1=seg_ticks, y0=0, y1=1),
                  textGrob(x=segs_center, y=0, 
                           label = seg_labels, hjust = .5, gp = gpar(cex =.7)))

# insert grobsTree in as annotation
g <- g + annotation_custom( grob = grobs,  
                            ymin = -.2, ymax = axis.y.pos, 
                            xmin = .25, xmax = 10.75)

# override clipping for plotting outside of plotting area
gt <- ggplot_gtable(ggplot_build(g))
gt$layout$clip[gt$layout$name == "panel"] <- "off"
grid.newpage()  
grid.draw(gt)

enter image description here

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