Plot 2D trajectories as variable-width lines

Creates a 2D line plot showing research trajectories over time, with highlighted trajectories displayed as variable-width lines and optional background trajectories shown in lowlight style. Edge widths grow along each highlighted trajectory based on cumulative paper counts, and labels are placed at trajectory endpoints.

Usage

plot_group_trajectories_lines_2d(
  traj_data,
  traj_filtered,
  title = "Main trajectories",
  width_range = c(0.8, 6),
  use_raw_papers = FALSE,
  label_nudge_x = 0.3,
  label_size = 4,
  show_only_highlighted = FALSE,
  lowlight_width = 0.9,
  lowlight_alpha = 0.22,
  lowlight_color = "#9AA5B1"
)

Arguments

traj_data

List containing trajectory data generated by detect_main_trajectories() with components:

• graph: igraph object containing nodes and edges across years

• trajectories: tibble of all candidate trajectories (traj_id + nodes list)

traj_filtered

Filtered trajectories tibble from filter_trajectories() containing the subset to emphasize. Must contain columns:

• traj_id: trajectory identifiers

• nodes: list of character vectors (ordered by time or orderable)

title

Plot title (default: "Main trajectories")

width_range

Range for edge widths of highlighted trajectories (default: c(0.8, 6.0)). Width at each segment is scaled by cumulative paper count up to the next node.

use_raw_papers

Whether to use raw paper counts for width scaling (default: FALSE). If TRUE, uses raw quantity_papers; if FALSE, uses weighted size: quantity_papers * prop_tracked_intra_group.

label_nudge_x

Horizontal nudge for trajectory end labels to prevent overlap with nodes (default: 0.30)

label_size

Text size for trajectory end labels (default: 4)

show_only_highlighted

Whether to show only highlighted trajectories (default: FALSE). If TRUE, hides all non-highlighted trajectory lines; if FALSE, draws lowlight background.

lowlight_width

Line width for lowlight (background) edges (default: 0.9)

lowlight_alpha

Transparency for lowlight edges (default: 0.22; smaller values = more transparent)

lowlight_color

Color for lowlight edges (default: "#9AA5B1" - neutral gray)

Value

A ggplot object displaying the trajectory network

Details

This function visualizes research trajectories as variable-width lines:

• Highlighted trajectories (traj_filtered) are colored lines with widths proportional to cumulative paper counts (raw or weighted)

• Background trajectories (when show_only_highlighted = FALSE) are shown as thin, transparent lines

• Trajectory labels are placed at the end of each highlighted trajectory

• The x-axis represents publication years using a Sugiyama layout

• The y-axis shows vertical positions from the layout (no intrinsic meaning)

• Colors are assigned only to highlighted trajectories present in the plot

When traj_data$trajectories is available and show_only_highlighted = FALSE, the lowlight layer shows only edges that belong to any trajectory but not the highlighted set. Otherwise, it shows the entire graph minus highlighted edges.

Examples

if (FALSE) { # \dontrun{
# Detect main trajectories first
traj_data <- detect_main_trajectories(your_graph_data)

# Filter trajectories of interest
filtered_traj <- filter_trajectories(traj_data$trajectories, 
                                     min_papers = 10)

# Create the plot
plot_group_trajectories_lines_2d(
  traj_data = traj_data,
  traj_filtered = filtered_traj,
  title = "Key Research Trajectories",
  width_range = c(1, 8),
  show_only_highlighted = FALSE
)
} # }