parcoords plots cannot handle date values

[RZachLamberty]

if you attempt to include a date dimension (standard datetime or numpy datetime64 objects) as one of the dimensions in the Parcoord graph object the resulting dimension is broken (no data points are included) and therefore so is the rest of the graph.

the following example will reproduce this behavior (plotly version 2.4.0, macos 10.13.3, conda distribution python 3.6.4):

import datetime
import numpy as np
import pandas as pd
import plotly.graph_objs as go
import plotly.offline

df = pd.DataFrame({
    'date': pd.date_range(start='2018-01-01', end='2018-12-31'),
    'value': np.random.random(365)
})
regular_dates = [
    datetime.datetime(2018, 1, 1) + datetime.timedelta(days=i)
    for i in range(365)
]

data1 = [
    go.Parcoords(
        dimensions=[
            {'values': df.date, 'label': 'date'},
            {'values': df.value, 'label': 'value'}
        ]
    )
]

# will fail to render correctly:
plotly.offline.plot(data1, filename='test1.html')

# just to be sure this isn't numpy date hell
data2 = [
    go.Parcoords(
        dimensions=[
            {'values': regular_dates, 'label': 'date'},
            {'values': df.value, 'label': 'value'}
        ]
    )
]

# also fails to render correctly:
plotly.offline.plot(data2, filename='test2.html')

both of these datasets (df.date and regular_dates) are perfectly acceptable inputs to other plotting types (e.g. go.Scatter).

[cldougl]

Hi there,
The values attribute must be a list of finite numbers. We note this in the description here: https://plot.ly/python/reference/#parcoords-dimensions-values however on the reference page we are autogenerating the type and have incorrectly rendered that a list of strings or datetimes is acceptable (sorry for the confusion, I've opened an issue here to fix that doc error: plotly/documentation#891).

For your chart, you can use the ticktext and tickvals attributes to display the dates as done for dimension C in this example: https://plot.ly/python/parallel-coordinates-plot/#adding-dimensions , however your values will have to be a list of finite numbers.

[harahu]

Not sure I unserstand why this issue was closed. It makes perfect sense to want to display datetimes and timedeltas as continuous values in a parallel coordinates plot.

I suggest opening it again and treating it as a feature request.

[alexcjohnson]

@harahu looks like this was closed as “oops, our docs implied that you could do this already, but we’re fixing that to make clear you can’t.”

I agree this would be a reasonable thing to want to do. Also real category data or even log axes. This would need to happen in plotly.js, where there’s already this issue: plotly/plotly.js#2292 - doesn’t specifically mention dates but that would be a natural extension.

That said, both issues have been dormant for 5 years so absent a code or $ contribution it’s unlikely to be acted upon any time soon.

[harahu]

Appreciate you pointing me in the right direction @alexcjohnson