Setting absolute size of facets in ggplot2

问题

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)

回答1:

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)

来源：https://stackoverflow.com/questions/32580946/setting-absolute-size-of-facets-in-ggplot2

标签

ggplot2

facet-wrap