CODEWITHSUNDEEP
rggplot2facet-wrap
erc
erc

Reputation: 10131

Setting absolute size of facets in ggplot2

I'm creating several facetted plots for a report. The number of facets varies between 2 and 8. Ideally, I'd like the absolute size of each facet (across plots) to be the same (e.g. 4x4 cm) so that it is easier to compare them (and it looks nicer, too).

Is that possible?

df1 <- structure(list(group1 = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L,1L, 1L, 1L, 1L, 1L), .Label = c("S1", "S2"), class = "factor"), group = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L), .Label = c("A", "B", "C", "D", "E"), class = "factor"), value = 1:12), class = "data.frame", row.names = c(NA, -12L), .Names = c("group1", "group", "value"))

df2 <- structure(list(group1 = structure(c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), .Label = c("S1", "S2"), class = "factor"), group = structure(c(4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L), .Label = c("A", "B", "C", "D", "E"), class = "factor"), value = 13:20), class = "data.frame", row.names = c(NA, -8L), .Names = c("group1", "group", "value"))

library(ggplot2)

plot1 <- ggplot(df1) + geom_histogram(aes(x=value)) + facet_wrap(~group)
plot2 <- ggplot(df2) + geom_histogram(aes(x=value)) + facet_wrap(~group)

enter image description here enter image description here

Upvotes: 15

Views: 2821

Answers (1)

baptiste
baptiste

Reputation: 77124

I've used the following function for this purpose,

set_panel_size <- function(p=NULL, g=ggplotGrob(p), file=NULL, 
                           margin = unit(1,"mm"),
                           width=unit(4, "cm"), 
                           height=unit(4, "cm")){

  panels <- grep("panel", g$layout$name)
  panel_index_w<- unique(g$layout$l[panels])
  panel_index_h<- unique(g$layout$t[panels])
  nw <- length(panel_index_w)
  nh <- length(panel_index_h)

if(getRversion() < "3.3.0"){

   # the following conversion is necessary
   # because there is no `[<-`.unit method
   # so promoting to unit.list allows standard list indexing
   g$widths <- grid:::unit.list(g$widths)
   g$heights <- grid:::unit.list(g$heights)

   g$widths[panel_index_w] <-  rep(list(width),  nw)
   g$heights[panel_index_h] <- rep(list(height), nh)

} else {

   g$widths[panel_index_w] <-  rep(width,  nw)
   g$heights[panel_index_h] <- rep(height, nh)

}

  if(!is.null(file))
    ggsave(file, g, 
           width = grid::convertWidth(sum(g$widths) + margin, 
                                unitTo = "in", valueOnly = TRUE),
           height = grid::convertHeight(sum(g$heights) + margin,  
                                  unitTo = "in", valueOnly = TRUE))

  g
}

g1 <- set_panel_size(plot1)
g2 <- set_panel_size(plot2)
gridExtra::grid.arrange(g1,g2)

enter image description here

Upvotes: 14

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