Callback Error updating figure in Plotly Dash – Dropdown and Output Figure

so today, I’m trying to create a simple dahsboard with data from multiple dataframes. I use the dropdown to select the dataframe to show in the plot. However, when I run this code, I got callback error in the web page says

Callback error updating loglog.figure
Traceback (most recent call last):
  File "C:UsersnaharAppDataLocalTemp/ipykernel_1556/982666652.py", line 63, in build_graph
    
TypeError: string indices must be integers

I don’t understand why this occurs, here is the code

logs = ['CALI','RDEP','GR','RHOB','NPHI','SP','DTC']
colors = ['black','firebrick','green','mediumaquamarine','royalblue','goldenrod','lightcoral']
log_cols = np.arange(1,8)


app = dash.Dash(__name__, external_stylesheets=[dbc.themes.SANDSTONE], meta_tags=[
        {"name": "viewport", "content": "width=device-width, initial-scale=1"}
    ])

server = app.server
app.config.suppress_callback_exceptions = True

app.layout = dbc.Container([
    dbc.Row([
        dbc.Col(html.H1('FORCE 2020 Well Log Challange Dashboard',
                        className='text-center mb-4'),
               width=12)
    ]),

    dbc.Row([
        dbc.Col([
            dcc.Dropdown(id='droplog',
                        options=[
                            {'label':'15/9-13','value':'well1'},
                            {'label':'15/9-15','value':'well2'},
                            {'label':'15/9-17','value':'well3'},
                            {'label':'16/1-2','value':'well4'},
                            {'label':'16/1-6 A','value':'well5'},
                            {'label':'16/10-1','value':'well6'},
                            {'label':'16/10-2','value':'well7'},
                            {'label':'16/10-3','value':'well8'},
                            {'label':'16/10-5','value':'well9'},
                            {'label':'16/11-1 ST3','value':'well10'},
                            {'label':'16/2-11 A','value':'well11'},
                            {'label':'16/2-16','value':'well12'}
                        ], multi=False, value='well1'),
            dcc.Graph(id='loglog',figure={})
        ])
        
    ]),

    dbc.Row([
        
    ])
])

@app.callback(
    Output(component_id='loglog',component_property='figure'),
    [Input(component_id='droplog',component_property='value')]
)

def build_graph(plot_chosen):
    logplot = make_subplots(rows=1, cols=len(logs), shared_yaxes=True)
    for i in range (len(logs)):
        
        if i == 1:
            logplot.add_trace(go.Scatter(x=plot_chosen[logs[i]], y=plot_chosen['DEPTH_MD'], 
                                         name=logs[i], line_color=colors[i]),row=1, col=log_cols[i])
            logplot.update_xaxes(type='log',row=1, col=log_cols[i], title_text=logs[i], 
                                 tickfont_size=12, linecolor='#585858')
        
        else:
            logplot.add_trace(go.Scatter(x=plot_chosen[logs[i]], y=plot_chosen['DEPTH_MD'], 
                                         name=logs[i], line_color=colors[i]),row=1, col=log_cols[i])
            logplot.update_xaxes(col=log_cols[i], title_text=logs[i],  linecolor='#585858')

    logplot.update_xaxes(showline=True, linewidth=2, linecolor='black', mirror=True, ticks='inside', tickangle= 0)
    logplot.update_yaxes(tickmode='linear', tick0=0,dtick=250, showline=True, linewidth=2, linecolor='black', 
                         mirror=True, ticks='outside')
    logplot.update_yaxes(row=1, col=1, autorange='reversed')
    logplot.update_layout(height=750, width=1200, showlegend=False)   
    logplot.update_layout(plot_bgcolor = "rgba(0,0,0,0)", paper_bgcolor = "rgba(0,0,0,0)")
    
    return logplot

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

and the input data used is in the form of many dataframes, one of which is like this for well 1

I tried to run defined function only, which build_graph, and it worked like a charm. The result of figure is shown here

Answer

I think I know what the problem is: the variable plot_chosen which is the argument in the function build_graph is a string. As a result you can not type y=plot_chosen['DEPTH_MD']. Although after choosing 15/9-13 on the Dropdown menu it has a value of well1, it does not represent the dataframe but a simple string. Try creating for example a dictionary with the dataframes

dataframes = {'well1': well1, 'well2': well2, ...}

and then choose the appropriate DataFrame from the dictionary.
So for example when the user chooses 15/9-13 on the dropdown you will get plot_chosen=’well1′ and you can simply get the dataframe well1 by using dataframes[plot_chosen].