user338714 user338714 - 24 days ago 13
R Question

How to dynamically wrap facet label using ggplot2

I'm looking for a way to dynamically wrap the strip label text in a

facet_wrap
or
facet_grid
call. I've found a way to accomplish this using
strwrap
, but I need to specify a
width
for the output to work as desired. Often the number of facets is not known in advance, so this method requires me to iteratively adjust the
width
parameter based on the dataset and plot size. Is it possible to dynamically specify a width for the wrap function, or is there another option for labeling facets that would work better?

library(ggplot2)
df = expand.grid(group=paste(c("Very Very Very Long Group Name "), 1:9),
x=rnorm(5), y=rnorm(5), stringsAsFactors=FALSE)

df$groupwrap = unlist(lapply(strwrap(df$group, width=30, simplify=FALSE), paste,
collapse="\n"))
p = ggplot(df) +
geom_point(aes(x=x, y=y)) +
facet_wrap(~groupwrap)


UPDATE: Based on the guidance provided by @baptiste and @thunk, I came up with the option below. Currently, it only works for a specified font family and size, but ideally, one should be able to also use the default
theme
settings. Maybe someone with more
ggplot2
experience has some suggestions for improvement.

library('grid')
grobs <- ggplotGrob(p)

sum = sum(sapply(grobs$width, function(x) convertWidth(x, "in")))
panels_width = par("din")[1] - sum # inches

df$group = as.factor(df$group)
npanels = nlevels(df$group)
if (class(p$facet)[1] == "wrap") {
cols = n2mfrow(npanels)[1]
} else {
cols = npanels
}

ps = 12
family = "sans"
pad = 0.01 # inches
panel_width = panels_width / cols
char_width = strwidth(levels(df$group)[
which.max(nchar(levels(df$group)))], units="inches", cex=ps / par("ps"),
family=family) / max(nchar(levels(df$group)))
width = floor((panel_width - pad)/ char_width) # characters

df$groupwrap = unlist(lapply(strwrap(df$group, width=width, simplify=FALSE),
paste, collapse="\n"))
ggplot(df) +
geom_point(aes(x=x, y=y)) +
facet_wrap(~groupwrap) +
theme(strip.text.x=element_text(size=ps, family=family))

Answer

Thanks to the guidance from @baptiste and @thunk, I created the function below, which seems to do a pretty good job of automatically wrapping facet labels. Suggestions for improvement are always welcome, though.

strwrap_strip_text = function(p, pad=0.05) { 
  # get facet font attributes
  th = theme_get()
  if (length(p$theme) > 0L)
    th = th + p$theme

  require("grid")
  grobs <- ggplotGrob(p)

  # wrap strip x text
  if ((class(p$facet)[1] == "grid" && !is.null(names(p$facet$cols))) ||
        class(p$facet)[1] == "wrap")
  {
    ps = calc_element("strip.text.x", th)[["size"]]
    family = calc_element("strip.text.x", th)[["family"]]
    face = calc_element("strip.text.x", th)[["face"]]

    if (class(p$facet)[1] == "wrap") {
      nm = names(p$facet$facets)
    } else {
      nm = names(p$facet$cols)
    }

    # get number of facet columns
    levs = levels(factor(p$data[[nm]]))
    npanels = length(levs)
    if (class(p$facet)[1] == "wrap") {
      cols = n2mfrow(npanels)[1]
    } else {
      cols = npanels
    }

    # get plot width
    sum = sum(sapply(grobs$width, function(x) convertWidth(x, "in")))
    panels_width = par("din")[1] - sum  # inches
    # determine strwrap width
    panel_width = panels_width / cols
    mx_ind = which.max(nchar(levs))
    char_width = strwidth(levs[mx_ind], units="inches", cex=ps / par("ps"), 
                          family=family, font=gpar(fontface=face)$font) / 
      nchar(levs[mx_ind])
    width = floor((panel_width - pad)/ char_width)  # characters

    # wrap facet text
    p$data[[nm]] = unlist(lapply(strwrap(p$data[[nm]], width=width, 
                                         simplify=FALSE), paste, collapse="\n"))
  }

  if (class(p$facet)[1] == "grid" && !is.null(names(p$facet$rows))) {  
    ps = calc_element("strip.text.y", th)[["size"]]
    family = calc_element("strip.text.y", th)[["family"]]
    face = calc_element("strip.text.y", th)[["face"]]

    nm = names(p$facet$rows)

    # get number of facet columns
    levs = levels(factor(p$data[[nm]]))
    rows = length(levs)

    # get plot height
    sum = sum(sapply(grobs$height, function(x) convertWidth(x, "in")))
    panels_height = par("din")[2] - sum  # inches
    # determine strwrap width
    panels_height = panels_height / rows
    mx_ind = which.max(nchar(levs))
    char_height = strwidth(levs[mx_ind], units="inches", cex=ps / par("ps"), 
                           family=family, font=gpar(fontface=face)$font) / 
      nchar(levs[mx_ind])
    width = floor((panels_height - pad)/ char_height)  # characters

    # wrap facet text
    p$data[[nm]] = unlist(lapply(strwrap(p$data[[nm]], width=width, 
                                         simplify=FALSE), paste, collapse="\n"))
  }

  invisible(p)
}

To use the function, call it in place of print.

library(ggplot2)
df = expand.grid(group=paste(c("Very Very Very Long Group Name "), 1:4),
                 group1=paste(c("Very Very Very Long Group Name "), 5:8),
                 x=rnorm(5), y=rnorm(5), stringsAsFactors=FALSE)

p = ggplot(df) +
  geom_point(aes(x=x, y=y)) +
  facet_grid(group1~group)
strwrap_strip_text(p)