清除所有 Dash dcc.Dropdown 问题

Question

So, I have this very simplified Dash app example. Code is below:

import pandas as pd
import dash
import dash_html_components as html
import dash_core_components as dcc
import plotly.express as px
from dash.dependencies import Input, Output

data = {'Fruits': ['apple',  'orange',  'banana'], 'Number': [10, 15, 7]}
df = pd.DataFrame(data, columns=['Fruits', 'Number'])
fruits_options = df['Fruits']

app = dash.Dash(__name__)

app.layout = html.Div(children=[
    html.H1(children='Fruits Bar Chart'),
    html.Div([
        dcc.Dropdown(
            id='dropdown',
            options=[{'label': i, 'value': i} for i in fruits_options],
            value='All Fruits',
            multi=True
         ),
        html.Div(dcc.Graph(id='graph')),
    ]),
])


@app.callback(
   Output(component_id='graph', component_property='figure'),
   Input(component_id='dropdown', component_property='value')
)
def update_graph(fruits):
    if 'All Fruits' in fruits:
        dff = df.copy()
    else:
        dff = df[df['Fruits'].isin(fruits)]

    figure = px.bar(dff, x=dff['Fruits'], y=dff['Number'])

    return figure


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

User can select multiple options and they will appear on the chart but when the user chose to clear all (x on the right side) it shows this error:

ValueError: Cannot accept list of column references or list of columns for both `x` and `y`.

Does anyone have a suggestion on how to fix this? Also, If possible I would like to return to the initial state of the chart when clear all is selected.

Thanks in advance.

Answer 1

The remove the error, you need to handle the case where fruits is an empty list. It could be as simple as replacing the

'All Fruits' in fruits

condition by

not fruits or 'All Fruits' in fruits

Since not fruits evaluates to True when the fruits variable is an empty list and your initial state was 'All Fruits' , this simple change should yield the desired outcome.