在ggplot2中设置facets的绝对大小

问题描述

我为报告创建了多个方面的图。理想情况下，我希望每个方面的绝对尺寸相同（例如4x4厘米），以便比较它们更容易（而且它看起来更好看）。

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).

这可能吗？

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)

推荐答案

这个目的，

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 = convertWidth(sum(g$widths) + margin,
                                unitTo = "in", valueOnly = TRUE),
           height = convertHeight(sum(g$heights) + margin,
                                  unitTo = "in", valueOnly = TRUE))

  g
}

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

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