[BUG] `dcc.Graph` `figure` prop may include Plotly.js `_inputArray` for typed arrays

まずサンプルの Dash アプリを実行し、ホバー前後の dcc.Graph の figure を調べます。typed-array データと _inputArray フィールドに重点を置いてください。dcc.Graph と Plotly.js 周辺の figure および callback の payload 処理を追跡します。_inputArray に対して選択した動作が一貫して実装され、typed-array における customdata の動作が考慮され、payload サイズが検証されていれば完了です。

When a dcc.Graph figure data contains typed arrays (for example int8, float32, etc.), the figure can include a Plotly.js internal field _inputArray

In the example below, the _inputArray is included after user interaction but not when the figure is first rendered.

_inputArray duplicates bdata and also includes decoded data, increasing callback payload size and overhead for large datasets.

Possible fixs:

• strip _inputArray in dcc.Graph before updating the figure prop. But that might be considered a breaking change since some people are now using _inputArray in callbacks.
• Have an option to not encode np arrays when using dash. This will also fix the issue of customdata not being available is clickData, hoverData if they are np arrays

Other related issues:

• Need a way to covert the typed arrays so the data is usable in a dash callback: https://github.com/plotly/dash/issues/3307

When app first renders (no _inputArray):

After hover (with _inputArray):

Sample App:

from dash import Dash, html, dcc, Input, Output
import numpy as np
import plotly.express as px
import json

app = Dash()

data = np.random.normal(0, 1, 250)
fig = px.histogram(data, nbins=20)

app.layout = html.Div([
    dcc.Graph(id="graph", figure=fig),
    html.Pre(id="fig-data")
])


@app.callback(
    Output("fig-data", "children"),
    Input("graph", "figure"),
    Input("graph", "hoverData"),
)
def debug(figure, hoverData):
    return json.dumps(figure["data"][0]["x"], indent=4)


if __name__ == "__main__":
    app.run(debug=True)