Plot multiple matrices in facets with different x-y axis - r

Question

I collected the data from a set of online forums and wanted to plot, using ggplot and facets (one facet per forum), the matrix that represent how many times user A replied to user B.
Here is the code to load a toy example:
library(ggplot2)
library(dplyr)
df.edges <- data.frame(from = c('forum1_user1', 'forum1_user1',
'forum1_user2', 'forum1_user2',
'forum2_user1', 'forum2_user1',
'forum2_user2', 'forum2_user2',
'forum3_user1', 'forum3_user1',
'forum3_user2', 'forum3_user2'),
to = c('forum1_user1', 'forum1_user2',
'forum1_user1', 'forum1_user2',
'forum2_user1', 'forum2_user2',
'forum2_user1', 'forum2_user2',
'forum3_user1', 'forum3_user2',
'forum3_user1', 'forum3_user2'),
weight = 1:12,
timestamp = 1:12,
subforum = c('forum1', 'forum1', 'forum1', 'forum1',
'forum2', 'forum2', 'forum2', 'forum2',
'forum3', 'forum3', 'forum3', 'forum3'))
I try this:
# Sort for later use in scale_discrete
df.edges <- df.edges %>% arrange(timestamp)
gg <- ggplot(df.edges, aes(x = from, y = to, fill = weight)) +
geom_raster() + coord_fixed() +
facet_grid(. ~subforum, scales='fixed') +
scale_x_discrete("from", aes(limits = from))+
scale_y_discrete("to", aes(limits = from)) +
theme_bw() +
theme(axis.line = element_blank(),
axis.text.x = element_text(angle = 90, hjust=1, size=8),
axis.text.y = element_text(hjust=1, size=10),
axis.ticks = element_blank(),
strip.background = element_rect(fill = 'white'),
aspect.ratio = 1) +
ggtitle("Matrix of interactions") + xlab('from') + ylab('to')
print(gg)
which gives this:
And if I set the facet scale scale='free':
However, I want each facet to show only those users belonging to that forum. The matrices should be completely filled with 4 cells in each one.
Any idea?

Answer 1

You could create a separate plot for each level of subforum and then lay them out together using grid.arrange:
library(gridExtra)
library(grid)
First, create the separate plots and store in a list. We add scale_fill_continuous(limits=range(df.edges$weight)) to ensure a consistent fill gradient across the three plots:
pl = lapply(split(df.edges, df.edges$subforum), function(df) {
ggplot(df, aes(x = from, y = to, fill = weight)) +
geom_raster() + coord_fixed() +
facet_grid(. ~subforum, scales='fixed') +
scale_x_discrete("from", aes(limits = from))+
scale_y_discrete("to", aes(limits = from)) +
scale_fill_continuous(limits=range(df.edges$weight)) +
theme_bw() +
theme(axis.line = element_blank(),
axis.text.x = element_text(angle = 90, hjust=1, size=8),
axis.text.y = element_text(hjust=1, size=10),
axis.ticks = element_blank(),
strip.background = element_rect(fill = 'white'),
aspect.ratio = 1) +
xlab('from') + ylab('to')
})
Extract the legend, as we want only one legend, rather than a separate legend for each plot:
# Function to extract legend
#https://github.com/hadley/ggplot2/wiki/Share-a-legend-between-two-ggplot2-graphs
g_legend<-function(a.gplot){
tmp <- ggplot_gtable(ggplot_build(a.gplot))
leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
legend <- tmp$grobs[[leg]]
return(legend) }
# Extract legend as a grob
leg = g_legend(pl[[1]])
Arrange the plots with legend and title:
grid.arrange(
textGrob("Matrix of Interactions"),
arrangeGrob(
arrangeGrob(grobs=lapply(pl, function(x) x + guides(fill=FALSE)), ncol=3),
leg, ncol=2, widths=c(10,1)
),
heights=c(1,20)
)