DashPlotly and Pandas choosing excel file via dropdown

Here is a method that works:

import dash
import dash_core_components as dcc
import dash_html_components as html
import plotly.graph_objects as go
import pandas as pd
import os

# 1. first create sample Excel files
data1 = [{'x': 1, 'y': 2}, {'x': 3, 'y': 4}]
data2 = [{'x': 10, 'y': -6}, {'x': -10, 'y': 8}]
pd.DataFrame(data1).to_excel('file1.xlsx', index=False)
pd.DataFrame(data2).to_excel('file2.xlsx', index=False)

# 2. read the Excel files and add a 'file_name' column
data_frames = []
for file_name in os.listdir():
    if file_name.endswith('.xlsx'):
        dfx = pd.read_excel(file_name)
        dfx['file_name'] = file_name
        data_frames.append(dfx)

# 3. concat the data frames
df = pd.concat(data_frames, axis=0)

excel_files = sorted(df['file_name'].unique().tolist())

# 4. dash code
app = dash.Dash()

fig_dropdown = html.Div([
    dcc.Dropdown(
        id='fig_dropdown',
        options=[{'label': x, 'value': x} for x in excel_files],
        value=excel_files[0]
    )])
fig_plot = html.Div(id='fig_plot')
app.layout = html.Div([fig_dropdown, fig_plot])

@app.callback(
  dash.dependencies.Output('fig_plot', 'children'),
  [dash.dependencies.Input('fig_dropdown', 'value')])
def name_to_figure(fig_name):
    dff = df[df.file_name == fig_name]
    figure = go.Figure()
    figure.add_trace(go.Scatter(y=dff.y, x=dff.x))
    return dcc.Graph(figure=figure)

app.run_server(debug=True, use_reloader=False)

1. We create 2 sample Excel files (you will not do this).
2. We read files ending in .xlsx.
   Then we turn the files into Pandas dataframes.
   Next, we add a column called 'file_name' to filter our data later.
3. We simply concatenate all the Excel files/ Padas dataframes.
4. We implement our Dash code.
   I used this example from Stack Overflow to help with this part.
   Here, we are using a callback function to update our figure.
   This is where we use the 'file_name' filter from above.
   Alternatively, you can read the Excel files directly instead of creating this filter.