Using dash upload component to upload csv file and generate a graph

Question

I want to upload a csv file and generate a graph that outputs the data from the csv file, I am able to upload the csv and display the data using dash_table, but I am unable to get the graph to work. My error after uploading the csv file: Invalid argument figure.data passed into Graph with ID "Mygraph". Expected an array. Was supplied type object.

import base64
import datetime
import io
import plotly.graph_objs as go
import cufflinks as cf

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

import pandas as pd

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

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

colors = {"graphBackground": "#F5F5F5", "background": "#ffffff", "text": "#000000"}

app.layout = html.Div(
    [
        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,
        ),
        dcc.Graph(id="Mygraph"),
        html.Div(id="output-data-upload"),
    ]
)


@app.callback(
    Output("Mygraph", "figure"),
    [Input("upload-data", "contents"), Input("upload-data", "filename")],
)
def update_graph(contents, filename):
    fig = {
        "layout": go.Layout(
            plot_bgcolor=colors["graphBackground"],
            paper_bgcolor=colors["graphBackground"],
        )
    }

    if contents:
        contents = contents[0]
        filename = filename[0]
        df = parse_data(contents, filename)
        df = df.set_index(df.columns[0])
        fig["data"] = df.iplot(
            asFigure=True, kind="scatter", mode="lines+markers", size=1
        )

    return fig


def parse_data(contents, filename):
    content_type, content_string = contents.split(",")

    decoded = base64.b64decode(content_string)
    try:
        if "csv" in filename:
            # Assume that the user uploaded a CSV or TXT 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))
        elif "txt" or "tsv" in filename:
            # Assume that the user upl, delimiter = r'\s+'oaded an excel file
            df = pd.read_csv(io.StringIO(decoded.decode("utf-8")), delimiter=r"\s+")
    except Exception as e:
        print(e)
        return html.Div(["There was an error processing this file."])

    return df


@app.callback(
    Output("output-data-upload", "children"),
    [Input("upload-data", "contents"), Input("upload-data", "filename")],
)


def update_table(contents, filename):
    table = html.Div()

    if contents:
        contents = contents[0]
        filename = filename[0]
        df = parse_data(contents, filename)

        table = html.Div(
            [
                html.H5(filename),
                dash_table.DataTable(
                    data=df.to_dict("rows"),
                    columns=[{"name": i, "id": i} for i in df.columns],
                ),
                html.Hr(),
                html.Div("Raw Content"),
                html.Pre(
                    contents[0:200] + "...",
                    style={"whiteSpace": "pre-wrap", "wordBreak": "break-all"},
                ),
            ]
        )

    return table


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

Error:

Answer 1

You need to create a go.Figure object and return it, e.g.:

@app.callback(Output('Mygraph', 'figure'), [
Input('upload-data', 'contents'),
Input('upload-data', 'filename')
])
def update_graph(contents, filename):
    x = []
    y = []
    if contents:
        contents = contents[0]
        filename = filename[0]
        df = parse_data(contents, filename)
        df = df.set_index(df.columns[0])
        x=df['DATE']
        y=df['TMAX']
    fig = go.Figure(
        data=[
            go.Scatter(
                x=x, 
                y=y, 
                mode='lines+markers')
            ],
        layout=go.Layout(
            plot_bgcolor=colors["graphBackground"],
            paper_bgcolor=colors["graphBackground"]
        ))
    return fig

Depending on what kind of graph you want (e.g. go.Scatter) and the type of values to display (x and y values). To add more lines to the plot, you can add more go.Scatter objects to data array with different values.