Clustermap

A clustermap composites a heatmap with optional row and column dendrograms into a single subplot — the seaborn sns.clustermap idiom. When trees are provided, rows and/or columns are automatically reordered to match the dendrogram leaf traversal order so cells align visually with the tree structure.

Basic clustermap (heatmap only)

double[,] data =
{
    { 0.1, 0.9, 0.3 },
    { 0.8, 0.2, 0.7 },
    { 0.4, 0.6, 0.5 },
};

var figure = Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax.Clustermap(data))
    .ToSvg(); // or .ToPng(), .Build(), ...

With row dendrogram

Add a RowTree whose leaves carry the original row indices in TreeNode.Value. The ClustermapSeries renderer will reorder the rows to match the DFS leaf traversal of the tree and render the dendrogram in the left panel.

var rowTree = new TreeNode
{
    Value = 2.0, // merge distance
    Children =
    [
        new TreeNode { Value = 0 }, // original row 0
        new TreeNode
        {
            Value = 1.0,
            Children =
            [
                new TreeNode { Value = 1 }, // original row 1
                new TreeNode { Value = 2 }, // original row 2
            ]
        }
    ]
};

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax.Clustermap(data, s =>
    {
        s.RowTree = rowTree;
        s.RowDendrogramWidth = 0.20; // fraction of total width, default 0.15
    }))
    .ToSvg();

With both dendrograms

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax.Clustermap(data, s =>
    {
        s.RowTree = rowTree;
        s.ColumnTree = colTree;
        s.RowDendrogramWidth = 0.15;      // default
        s.ColumnDendrogramHeight = 0.15;  // default
    }))
    .ToSvg();

Custom colormap and labels

using MatPlotLibNet.Styling.ColorMaps;

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax.Clustermap(data, s =>
    {
        s.ColorMap = ColorMaps.RdBu;
        s.ShowLabels = true;
        s.LabelFormat = "F2";
    }))
    .ToSvg();

Tree leaf convention

Leaf TreeNode.Value must be the zero-based original index of the row or column in the data matrix (e.g. 0, 1, 2 for a 3-row matrix). Internal nodes carry the merge distance (any positive double). If the tree is malformed (out-of-range indices, duplicates, or wrong count) ResolveLeafOrder falls back to the identity order silently.

// A valid 3-row tree: leaves have Value = original index
var validTree = new TreeNode
{
    Value = 2.0,
    Children =
    [
        new TreeNode { Value = 2 }, // row 2 comes first in display order
        new TreeNode
        {
            Value = 1.0,
            Children =
            [
                new TreeNode { Value = 0 }, // then row 0
                new TreeNode { Value = 1 }, // then row 1
            ]
        }
    ]
};
// Resulting display order: row 2, row 0, row 1

Panel ratios

Property	Type	Default	Range	Effect
`RowDendrogramWidth`	`double`	`0.15`	`[0.0, 0.9]`	Fraction of width for row dendrogram. `0` suppresses it.
`ColumnDendrogramHeight`	`double`	`0.15`	`[0.0, 0.9]`	Fraction of height for column dendrogram. `0` suppresses it.

Values are clamped on assignment; no exception is thrown for out-of-range inputs.

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