Automatic adjustment of margins in horizontal bar chart

Question

I need to produce a series of horizontal grouped bar charts. The barplot function does not automatically adjust the margins of the plot, therefore the text gets cut off.

  graphics.off()      # close graphics windows
   test <- matrix(c(55,65,30, 40,70,55,75,6,49,45,34,20), 
                  nrow =3 , 
               ncol=4, 
               byrow=TRUE,
               dimnames = list(c("Subgroup 1", "Subgroup 2", "Subgroup 3"),
                               c(
                                 "Category 1 Long text",
                                 "Category 2 very Long text",
                                 "Category 3 short text",
                                 "Category 4 very short text"
                                 )))
  barplot(test, 
       las=2,
       beside = TRUE,
       legend=T,
       horiz=T)

I can't find an option to automatically move the plot further to the right, the way R dotchart function does it ( (barchart procedure in SAS adjusts the margins automatically as well). Obviously, I can always adjust the margins manually using par function.

  par(mar=c(5.1, 13 ,4.1 ,2.1))

will move the plot to the right

Is there an option to move the plot to the right (i.e. adjust the margins) automatically depending on the length of the text?

I can think of 2 related appproaches to do it programmatically: 1) Calculate the length of the longest text string and accordingly adjust the left margin 2) Create a dotchart plot for the data, somehow capture the margins and use the same margins in bar chart.

Is there an easier way to do it? Thanks!

Answer 1

I think your first idea is probably the most appropriate. Something like this seems to work okay and requires not much stuffing about.

ylabels <-  c(  "1oooooooooooo",
            "2",
            "3",
            "4"
)

test <- matrix(c(55,65,30, 40,70,55,75,6,49,45,34,20), 
                  nrow =3 , 
               ncol=4, 
               byrow=TRUE,
               dimnames = list(c("Subgroup 1", "Subgroup 2", "Subgroup 3"),
                               ylabels))

# adjust to the maximum of either the default 
# or a figure based on the maximum length
par(mar=c(5.1, max(4.1,max(nchar(ylabels))/1.8) ,4.1 ,2.1))

barplot(test, 
       las=2,
       beside = TRUE,
       legend=T,
       horiz=T)

After inspecting dotchart, a more generalisable solution may also be to use:

linch <-  max(strwidth(ylabels, "inch")+0.4, na.rm = TRUE)
par(mai=c(1.02,linch,0.82,0.42))