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Create flow transitions for bidirectional Sankey diagrams

Source: R/gg_sankey_utils.R
make_flows.Rd

Processes intervention scaling data to generate flow transitions between nodes in both upward (adding interventions) and downward (removing interventions) directions. Calculates flow positions, coordinates, and label placements while minimizing visual crossings through intelligent sorting algorithms.

Usage

make_flows(x, nodes)

Arguments

x

Data frame containing intervention scaling data where columns represent different intervention states (named with numeric values: negative for removal steps, 0 for current state, positive for addition steps) and rows represent individual flow paths through the intervention scaling process

nodes

Data frame containing node information

Value

Data frame containing detailed flow information with columns:

  • flow_start, flow_end: Character. Source and destination node names

  • direction: Character. Flow direction ("up" or "down")

  • n: Integer. Number of individual transitions for this flow

  • *_start, *_end: Numeric. Coordinate boundaries for flow start and end points

  • flow_start_center, flow_end_center: Numeric. Center positions of flows

  • label_x, label_y: Numeric. Optimal label positioning coordinates

  • hjust: Numeric. Horizontal text alignment (0 for left, 1 for right)

  • flow_label: Character. Custom flow descriptions (if available in flow_labels)

Details

The function performs several key operations:

  • Identifies upward transitions (positive column progressions) representing intervention additions

  • Identifies downward transitions (negative column progressions) representing intervention removals

  • Calculates flow frequencies and positions within source and destination nodes

  • Applies intelligent sorting to minimize visual flow crossings

  • Determines appropriate label positioning and alignment based on flow direction

  • Joins with external flow_labels data for custom flow descriptions

Flow positioning uses a two-pass sorting algorithm: first sorting flows within each source node by destination position, then sorting flows within each destination node by source position. This approach significantly reduces visual crossing of flow ribbons in the final Sankey diagram.