How to work on selected column from drop down of all the columns of dataset?

Dash Python
1

Hi.
Below is my code. Currently it has 3 functions to perform:

  • User selects the file type.
  • User uploads the data which is displayed on the screen.
  • A dropdown for selecting a particular column of the dataset.

Now I want to perform operations on that selected column but i do not know the way to extract it into a new variable.

import base64
import datetime
import io

import dash
from dash.dependencies import Input, Output, State
from dash import dcc, html, dash_table

import pandas as pd

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = dash.Dash(__name__, external_stylesheets=external_stylesheets)

app.layout = html.Div([
    dcc.Dropdown(['Excel Sheet', 'CSV File'], id='file_type', multi=False, style={'width': "40%"}),
    html.Div(id='output_filetype'),
    dcc.Upload(
        id='upload-data',
        children=html.Div([
            'Drag and Drop or ',
            html.A('Select Files')
        ]),
        style={
            'width': '100%',
            'height': '60px',
            'lineHeight': '60px',
            'borderWidth': '1px',
            'borderStyle': 'dashed',
            'borderRadius': '5px',
            'textAlign': 'center',
            'margin': '10px'
        },
        # Allow multiple files to be uploaded
        multiple=True
    ),
    html.Div(id='output-data-upload'),
    html.Div(id='column_dropdown'),
])

def parse_contents(contents, filename, date):
    content_type, content_string = contents.split(',')
    #global df
    decoded = base64.b64decode(content_string)
    try:
        if 'csv' in filename:
            # Assume that the user uploaded a CSV file
            df = pd.read_csv(
                io.StringIO(decoded.decode('utf-8')))
        elif 'xls' in filename:
            # Assume that the user uploaded an excel file
            df = pd.read_excel(io.BytesIO(decoded))

        app.layout = html.Div([
            dcc.Dropdown(
                [{'name': i, 'id': i} for i in df.columns], id='file_type', multi=False, style={'width': "40%"}
            ),
            html.Div(id='output_filetype'),])

    except Exception as e:
        print(e)
        return html.Div([
            'There was an error processing this file.'
        ])


    ####### Dropdown #########



    return html.Div([
        html.H5(filename),
        html.H6(datetime.datetime.fromtimestamp(date)),

        dash_table.DataTable(
            df.to_dict('records'),
            [{'name': i, 'id': i} for i in df.columns]
        ),

        html.Hr(),  # horizontal line

        # For debugging, display the raw contents provided by the web browser
        html.Div('Raw Content'),
        html.Pre(contents[0:200] + '...', style={
            'whiteSpace': 'pre-wrap',
            'wordBreak': 'break-all'
        })
    ])


def selectData(contents, filename, date):

    content_type, content_string = contents.split(',')
    decoded = base64.b64decode(content_string)

    try:
        if 'csv' in filename:
            # Assume that the user uploaded a CSV file
            df = pd.read_csv(
                io.StringIO(decoded.decode('utf-8')))
        elif 'xls' in filename:
            # Assume that the user uploaded an excel file
            df = pd.read_excel(io.BytesIO(decoded))

        Dropdown = html.Div([
                            html.H4(('File Name: ', filename), style={'width': '100%', 'textAlign': 'center'}),
                            html.Br(),
                            dcc.Dropdown(
                                id='Dataset_and_Column',
                                options=[{'label': i, 'value': i} for i in df.columns],
                                style={'width': '100%', 'height': '60px', 'lineHeight': '60px', 'borderWidth': '1px',
                                       'borderStyle': 'dashed', 'borderRadius': '5px', 'textAlign': 'center', 'display': 'inline-block'},
                                placeholder='Select Dataset Column'
                            ),
                            html.Br(),
                    ])
        return Dropdown
    except Exception as e:
        print(e)
        return html.Div([
            'There was an error processing this file.'
        ])



@app.callback(Output('output_filetype', 'children'),
              Output('output-data-upload', 'children'),
              Output('column_dropdown', 'children'),
              Input(component_id='file_type', component_property='value'),
              Input('upload-data', 'contents'),
              State('upload-data', 'filename'),
              State('upload-data', 'last_modified'))

def update_output(value, list_of_contents, list_of_names, list_of_dates):
    container = "{}".format(value)
    if list_of_contents is not None and value is not None:
        Dropdown = [selectData(c, n, d) for c, n, d in zip(list_of_contents, list_of_names, list_of_dates)]
        children = [
            parse_contents(c, n, d) for c, n, d in
            zip(list_of_contents, list_of_names, list_of_dates)]
        return container, children, Dropdown
    else:
        return '','',''




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