Plotly Express error with subset categorical pandas column

[kvanderwijst]

Plotly Express gives a KeyError when using a subselection of a dataframe with a categorical column. The categorical column is useful for custom ordering of values, but sometimes you only want to plot a subset of that dataframe. When not all the values of the Categorical column are present in the subselection, Plotly Express gives an error:

df = pd.DataFrame({
    "x": [0, 0, 1, 0, 1],
    "Value": [10, 5, 7, 3, 8],
    "Category": pd.Categorical(["one", "two", "one", "three", "three"], categories=["one", "two", "three"], ordered=True)
})

px.scatter(
    df[df["Category"].isin(["one", "three"])],  # Works fine with just `df` here
    x="x",
    y="Value",
    color="Category"
)