Add aspect ratio support in ggdesplot (not completely sure)

[SchmidtPaul]

Summary

This PR adds support for the aspect parameter in ggdesplot() to control cell aspect ratios for true-scale field maps.

Note that this PR is also kind of an issue - see "Observation on Lattice Behavior" below

The aspect ratio feature is documented for the lattice version with the note "To get a map of a field with a true aspect ratio (lattice version only), include 'aspect=ylen/xlen'". This PR removes the "lattice version only" limitation by implementing aspect ratio support for the ggplot2 version.

Changes

R/ggdesplot.R:

• Added aspect parameter to function signature (line 81)
• Implemented aspect ratio logic using coord_fixed(ratio=aspect, expand=FALSE) when aspect is specified (lines 530-536)
• When aspect is NULL, uses coord_cartesian(expand=FALSE) as before (default behavior unchanged)

R/desplot.R:

• Updated the call to ggdesplot() to pass ... arguments through (line 330)
• This allows aspect (and other future parameters) to flow from desplot(gg=TRUE) to ggdesplot()

Implementation Details

The implementation uses coord_fixed(ratio=aspect) where aspect represents the height/width ratio. Both lattice and ggplot2 use this same convention:

• aspect=1 → square cells
• aspect=2 → cells 2x taller than wide
• aspect=0.5 → cells 2x wider than tall

Observation on Lattice Behavior

During development and testing, I observed something unexpected: when using ggdesplot() with aspect=1, the cells appear square (as expected). However, when using the lattice version desplot() with aspect=1, the cells do not appear square.

I wanted to bring this to your attention because:

1. I may be misunderstanding how the aspect parameter is intended to work in the lattice version
2. There may be a difference in how lattice and ggplot2 interpret aspect ratios that I'm not aware of
3. It's possible this represents an area where the implementations naturally differ

The ggplot2 implementation uses coord_fixed(ratio=aspect) which directly controls the ratio of y-axis units to x-axis units, creating cell shapes that correspond to the aspect value as I understand it.

Reprex

library(desplot)
library(agridat)

desplot(
  yates.oats,
  yield ~ col * row,
  col = gen,
  num = nitro,
  cex = 1,
  out1 = block,
  aspect = 1,
  gg = FALSE,
  main = "aspect=1, gg=FALSE"
)

desplot(
  yates.oats,
  yield ~ col * row,
  col = gen,
  num = nitro,
  cex = 1,
  out1 = block,
  aspect = 1,
  gg = TRUE,
  main = "aspect=1, gg=TRUE"
)

desplot(
  yates.oats,
  yield ~ col * row,
  col = gen,
  num = nitro,
  cex = 1,
  out1 = block,
  aspect = 0.5,
  gg = FALSE,
  main = "aspect=0.5, gg=FALSE"
)

desplot(
  yates.oats,
  yield ~ col * row,
  col = gen,
  num = nitro,
  cex = 1,
  out1 = block,
  aspect = 0.5,
  gg = TRUE,
  main = "aspect=0.5, gg=TRUE"
)

cat(
  "Testing with desplot version:",
  as.character(packageVersion("desplot")),
  "\n"
)
#> Testing with desplot version: 1.11

^{Created on 2025-11-14 with reprex v2.1.1}

Benefits

• Enables true-scale field mapping with ggdesplot()
• Brings ggplot2 version closer to feature parity with lattice version
• Cells correctly scale according to aspect ratio value
• Default behavior unchanged when aspect is not specified

[kwstat]

I'm adding a better example to desplot.R file:

data(yates.oats)
# Show experiment layout in true aspect
# Field width = 4 plots * 44 links = 176 links
# Field length = 18 plots * 28.4 links = 511 links
# With lattice, the aspect ratio is y/x for the entire field
desplot(yates.oats, 
        yield ~ col+row, 
        out1=block, out2=gen, aspect=511/176)
# With ggplot, the aspect ratio is y/x for each cell
ggdesplot(yates.oats, 
        yield ~ col+row, 
        out1=block, out2=gen, aspect=28.4/44)