Labels do not align correctly in 12 panel figure using Cowplot - plot_grid

[czq2007hlj]

I used plot_grid to generate a 12 (3 row by 4 col) panel figure, however, I was not able to get the alignment correct for the 3rd row after "hjust = -6".
Thank you for your time and help!

PP1 <- ggplot(mpg, aes(x = cty, y = hwy, colour = factor(cyl))) + geom_point(size = 2.5)
....

PP12 <- ggplot(mpg, aes(x = cty, y = hwy, colour = factor(cyl))) + geom_point(size = 2.5)

plot3by4 <- plot_grid(PP1, PP2, PP3, PP4, PP5, PP6, PP7, PP8, PP9, PP10, PP11, PP12, labels=c("A", "B", "C", "D","E", "F", "G", "H", "I", "J", "K", "L"), ncol = 4, nrow = 3, align = 'v', hjust=-6, label_size=17)

save_plot("plot3by4.png", plot3by4, ncol = 4, nrow = 3, base_aspect_ratio = 1 )

[clauswilke]

Apparently this is caused by the fact that the label font is proportional width. The effect of hjust depends on the width of the label, and that width varies. In particular, the label "I" is very narrow, so the effect is biggest there.

You can see that if all labels are the same, then there is no problem:

plot3by4 <- plot_grid(PP1, PP2, PP3, PP4, PP5, PP6, PP7, PP8, PP9, PP10, PP11, PP12,
                      labels=c("A", "A", "A", "A","A", "A", "A", "A", "A", "A", "A", "A"),
                      ncol = 4, nrow = 3, align = 'v', hjust=-6, label_size=17)
plot3by4

Of course that won't help you much. One solution would be to provide individual hjust values for each label, by making hjust a vector of length 12. That is possible but ugly. Alternatively, I would recommend adding the labels manually, like so:

xoff <- .35 # relative x position of label, within one plot
yoff <- .93 # relative y position of label, within one plot
plot3by4 <- plot_grid(PP1, PP2, PP3, PP4, PP5, PP6, PP7, PP8, PP9, PP10, PP11, PP12,
                      ncol = 4, nrow = 3, align = 'v') +
            draw_plot_label(label=c("A", "B", "C", "D","E", "F", "G", "H", "I", "J", "K", "L"),
                            x=rep((xoff+0:3)/4, 3),
                            y=1-(1-yoff+rep(0:2, each=4))/3,
                            hjust=.5, vjust=.5, size=17)
plot3by4

Thanks for pointing this out. I wasn't aware of this issue, and I may have to modify the way label placement is done in plot_grid.

[czq2007hlj]

Perfect.
Thank you so much for such a prompt reply!

[clauswilke]

This problem is now permanently solved in cowplot devel through the addition of the label_x and label_y arguments to plot_grid():

plot3by4 <- plot_grid(PP1, PP2, PP3, PP4, PP5, PP6, PP7, PP8, PP9, PP10, PP11, PP12,
     labels = "AUTO", ncol = 4, nrow = 3, label_x = .3, hjust = 0, label_size=17)