DASH回调更新graph.figure报错：邮编选择后直方图异常

错误原因与修复点 #

• 数据类型错误：dropdown_changed函数的else分支中，datalist2 = datalist[datalist['Postcode'].isin(postcodes)], 末尾多了一个逗号，导致datalist2变成包含DataFrame的元组，而非直接的DataFrame，传给px.histogram时会因类型不匹配报错，需删除该逗号。
• 颜色逻辑覆盖：原代码中统一执行fig.update_traces(marker=dict(color="#002664"))，会覆盖color='Postcode'的颜色区分效果，导致选中邮编后无法看到不同邮编的颜色差异，需仅在默认无选中状态时保留该设置。
• 冗余代码优化：原代码中pd.Series(datalist['Postcode'].unique()).sort_values(ascending=True)未赋值给变量，属于无效代码，可简化为sorted(datalist['Postcode'].unique())生成排序后的邮编列表。

修正后完整代码 #

import pandas as pd
import plotly.express as px
from dash import Dash, html, dcc, Input, Output


app = Dash(__name__)
app.title = "EGMs in NSW"

# 加载数据
datalist = pd.read_excel('premises-list-Aug-2022.xlsx', skiprows=[0,1,2])
datalist['Licence type'] = datalist['Licence type'].str.split(" - ").str.get(1)
datalist['Licence type'] = datalist['Licence type'].str.title()

# 生成去重并排序的邮编列表
postcode = sorted(datalist['Postcode'].unique())

def make_histogram_plot():
    fig = px.histogram(
        data_frame=datalist,
        x='Licence type', 
        y='EGMs', 
        color='Postcode',
        title='EGMs by Licence Type in NSW',
        histfunc='avg'
    )
    # 默认状态下统一颜色
    fig.update_traces(marker=dict(color="#002664"))
    fig.update_layout(
        plot_bgcolor='#EAEDF4',
        xaxis_title=None,
        yaxis_title='Average EGMs'
    )
    return fig

app.layout = html.Div(children=[
    html.Div([
        dcc.Dropdown(postcode, value=[], placeholder="Select postcodes", multi=True, id='postcodes')
    ]),
    dcc.Graph(id='graph', figure=make_histogram_plot())
])

@app.callback(
    Output('graph', 'figure'),
    Input('postcodes', 'value')
)
def dropdown_changed(postcodes):
    if postcodes == []:
        fig = make_histogram_plot()
    else:
        datalist2 = datalist[datalist['Postcode'].isin(postcodes)]
        fig = px.histogram(
            data_frame=datalist2,
            x='Licence type', 
            y='EGMs', 
            color='Postcode',
            title='EGMs by Licence Type in NSW',
            histfunc='avg'
        )
        fig.update_layout(
            plot_bgcolor='#EAEDF4',
            xaxis_title=None,
            yaxis_title='Average EGMs'
        )
    return fig

if __name__ == '__main__':
    app.run_server(debug=True)

内容的提问来源于stack exchange，提问作者ZJJ