TRIANGULAR_HEATMAP

Excel Usage

=TRIANGULAR_HEATMAP(data, title, color_map, triangle, values, colorbar)
  • data (list[list], required): Input matrix data.
  • title (str, optional, default: null): Chart title.
  • color_map (str, optional, default: “viridis”): Color map.
  • triangle (str, optional, default: “lower”): Triangle part (‘lower’, ‘upper’).
  • values (str, optional, default: “false”): Show values.
  • colorbar (str, optional, default: “true”): Show colorbar.

Returns (object): Matplotlib Figure object (standard Python) or base64 encoded PNG string (Pyodide).

Examples

Example 1: Lower triangular heatmap

Inputs:

data triangle
1 2 3 lower
4 5 6
7 8 9

Excel formula:

=TRIANGULAR_HEATMAP({1,2,3;4,5,6;7,8,9}, "lower")

Expected output:

"chart"

Example 2: Upper triangular heatmap

Inputs:

data triangle
1 2 3 upper
4 5 6
7 8 9

Excel formula:

=TRIANGULAR_HEATMAP({1,2,3;4,5,6;7,8,9}, "upper")

Expected output:

"chart"

Example 3: Triangular heatmap with title

Inputs:

data title triangle
1 2 My Triangle lower
3 4

Excel formula:

=TRIANGULAR_HEATMAP({1,2;3,4}, "My Triangle", "lower")

Expected output:

"chart"

Example 4: Triangular heatmap showing values

Inputs:

data triangle values
1.5 2.5 3.5 lower true
4.5 5.5 6.5
7.5 8.5 9.5

Excel formula:

=TRIANGULAR_HEATMAP({1.5,2.5,3.5;4.5,5.5,6.5;7.5,8.5,9.5}, "lower", "true")

Expected output:

"chart"

Python Code

import sys
import matplotlib
IS_PYODIDE = sys.platform == "emscripten"
if IS_PYODIDE:
    matplotlib.use('Agg')
import matplotlib.pyplot as plt
import io
import base64
import numpy as np

def triangular_heatmap(data, title=None, color_map='viridis', triangle='lower', values='false', colorbar='true'):
    """
    Create a lower or upper triangular heatmap.

    See: https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.imshow.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        data (list[list]): Input matrix data.
        title (str, optional): Chart title. Default is None.
        color_map (str, optional): Color map. Valid options: Viridis, Plasma, Inferno, Magma, Cividis. Default is 'viridis'.
        triangle (str, optional): Triangle part ('lower', 'upper'). Valid options: Lower, Upper. Default is 'lower'.
        values (str, optional): Show values. Valid options: True, False. Default is 'false'.
        colorbar (str, optional): Show colorbar. Valid options: True, False. Default is 'true'.

    Returns:
        object: Matplotlib Figure object (standard Python) or base64 encoded PNG string (Pyodide).
    """
    def to2d(x):
        return [[x]] if not isinstance(x, list) else x

    try:
        data = to2d(data)

        if not isinstance(data, list) or not all(isinstance(row, list) for row in data):
            return "Error: Invalid input - data must be a 2D list"

        # Convert to numpy array
        try:
            arr = np.array(data, dtype=float)
        except (ValueError, TypeError) as e:
            return f"Error: Could not convert data to numeric array: {str(e)}"

        if arr.ndim != 2:
            return "Error: Data must be a 2D array"

        if arr.size == 0:
            return "Error: Data array is empty"

        # Create mask for triangular display
        mask = np.zeros_like(arr, dtype=bool)
        if triangle.lower() == "lower":
            # Mask upper triangle
            mask = np.triu(np.ones_like(arr, dtype=bool), k=1)
        elif triangle.lower() == "upper":
            # Mask lower triangle
            mask = np.tril(np.ones_like(arr, dtype=bool), k=-1)
        else:
            return f"Error: Invalid triangle parameter '{triangle}'. Must be 'lower' or 'upper'"

        # Apply mask by setting to NaN
        arr_masked = arr.copy()
        arr_masked[mask] = np.nan

        # Create figure
        fig, ax = plt.subplots(figsize=(8, 6))

        # Create heatmap
        im = ax.imshow(arr_masked, cmap=color_map, aspect='auto')

        # Add colorbar if requested
        show_colorbar = colorbar.lower() == "true"
        if show_colorbar:
            plt.colorbar(im, ax=ax)

        # Add values if requested
        show_values = values.lower() == "true"
        if show_values:
            for i in range(arr.shape[0]):
                for j in range(arr.shape[1]):
                    if not mask[i, j]:
                        text = ax.text(j, i, f'{arr[i, j]:.2f}',
                                     ha="center", va="center", color="white")

        # Set labels
        if title:
            ax.set_title(title)

        plt.tight_layout()

        # Return based on environment
        if IS_PYODIDE:
            buf = io.BytesIO()
            plt.savefig(buf, format='png', dpi=100, bbox_inches='tight')
            buf.seek(0)
            img_base64 = base64.b64encode(buf.read()).decode('utf-8')
            plt.close(fig)
            return f"data:image/png;base64,{img_base64}"
        else:
            return fig
    except Exception as e:
        return f"Error: {str(e)}"

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