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Python Dash application with drop down menu that selects excel file sheets and displays in a table

Posted by: admin April 23, 2020 Leave a comment

Questions:

I am in the process of learning Dash with the final goal being the development of an app that allows quick analysis of data sets in an excel file. I’d like a drop down menu that will allow for switching between the sheets in the excel file. I’m having trouble getting this to run properly. I can make it output to a graph but not a table. My code is as follows:

import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html
import dash_table_experiments as dt
import pandas as pd

app = dash.Dash()

df = pd.read_excel('output.xlsx', sheet_name=None)

app.layout = html.Div(
    html.Div([dcc.Dropdown(id='drop_value',
                           options=[{'label': i, 'value': i} for i in df],
                           value='Sheet1')]),
    html.Div([dt.DataTable(rows=[{}],
                           id='table')])
)


@app.callback(Output('table', 'rows'), [Input('drop_value', 'value')])
def update_info_table(drop_value):
    if drop_value == 'Sheet1':
        new_data = df['Sheet1'].to_dict()
        return new_data
    elif drop_value == 'Sheet2':
        new_data = df['Sheet2'].to_dict()
        return new_data
    else:
        new_data = df['Sheet3'].to_dict()
        return new_data


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

When I run this code I get the following error:
TypeError: init() takes from 1 to 2 positional arguments but 3 were given

I’m assuming this has something to do with the format of the dataset I’m trying to feed to the datatable. Right now I’m just using a dummy excel file with only two columns labeled ‘x1’ and ‘y1’.

How to&Answers:

Adjusted code and seems to work now. Correct code is below for anyone who needs.

import dash
import dash_core_components as dcc
import dash_html_components as html
import pandas as pd
import dash_table_experiments as dt

# Load in data set
sheet_to_df_map = pd.ExcelFile('output.xlsx')
dropdown_options = pd.read_excel('output.xlsx', sheet_name=None)

# Create the dash app
app = dash.Dash()

# Define the layout for the drop down menu
app.layout = html.Div([
    html.H2("Select Sheet Number"),
    html.Div([dcc.Dropdown(id="field_dropdown", options=[{
                               'label': i,
                               'value': i
                           } for i in dropdown_options],
                           value='Sheet3')],
             style={'width': '25%',
                    'display': 'inline-block'}),
    dt.DataTable(rows=[{}],
                 row_selectable=True,
                 filterable=True,
                 sortable=True,
                 selected_row_indices=[],
                 id='datatable')
])


@app.callback(
    dash.dependencies.Output('datatable', 'rows'),
    [dash.dependencies.Input('field_dropdown', 'value')])
def update_datatable(user_selection):
    if user_selection == 'Sheet1':
        return sheet_to_df_map.parse(0).to_dict('records')
    elif user_selection == 'Sheet2':
        return sheet_to_df_map.parse(1).to_dict('records')
    else:
        return sheet_to_df_map.parse(2).to_dict('records')


if __name__ == '__main__':
    app.run_server()code here