Parallel coordinates

Reshapes the plot data so that the selected columns become parallel vertical axes. Each observation is drawn as a polyline connecting its values across all axes. Values are optionally normalised per column to share a common 0-1 scale.

Usage

project_parallel(
  plot,
  columns = NULL,
  group = NULL,
  scale = c("std", "global", "none"),
  order = NULL,
  recenter = NULL,
  aggregate = c("none", "mean", "median"),
  axis_labels = TRUE,
  alpha = 0.2,
  size = 1,
  ...
)

Arguments

plot

A plotit object.

columns

Character vector of column names to use as parallel axes. Order matters: the first column is the leftmost axis.

group

Column name for colouring lines. NULL = no grouping.

scale

"std" (default): min-max normalise each column to 0-1. "global": min-max normalise across all columns to 0-1. "none": no normalisation, each column keeps its own range.

order

Axis order: character subset of columns; axes render in the given order and omitted columns drop. NULL (default) keeps the columns order.

recenter

Reference axis for a difference-from-reference view: a column name; every polyline is re-expressed as its difference from that axis (normalised space), so the reference becomes a straight zero baseline. NULL disables.

aggregate

Group overlay: "none" (default), or "mean" / "median" to draw one thick aggregate line per group behind the individual polylines (requires group).

axis_labels

Draw the per-axis tick labels (default TRUE); FALSE blanks them for a clean silhouette view.

alpha, size

Passed to geom_line() / geom_point().

...

Passed to geom_line().

Value

Modified plotit object.

Details

Adds geom_line() and geom_point() layers. Call after any mark_* layers that should sit beneath the parallel-coordinate lines.

Examples

plotit(iris, encode()) |>
  project_parallel(columns = c("Sepal.Width", "Sepal.Length", "Petal.Width", "Petal.Length"))