Visually marking numpy's NaN as grey

šŸ“Š Plotly Python
1

Using the surface object, how can I make NaNā€™s grey? (a color not in the colorscale that I am using (RdBu))

2

Hi @gekko102,

I think youā€™ll need to convert the nan values to some other value and then use a custom colorscale.

Hereā€™s an example

import plotly.plotly as py
import plotly.graph_objs as go
import numpy as np
import copy

import pandas as pd

# Read data from a csv
z_data = pd.read_csv('https://raw.githubusercontent.com/plotly/datasets/master/api_docs/mt_bruno_elevation.csv')
z=z_data.values.copy()

# Compute surface color with nan's
surfacecolor = z.copy()
surfacecolor[-10:, -10:] = np.nan

# Replace nans with -100
surfacecolor[np.isnan(surfacecolor)] = -100

# Build surface trace
data = [
    go.Surface(
        z=z,
        surfacecolor=surfacecolor,
        cmin = -5,
        cmax = 350,
        colorscale=[[0, 'gray'],
                    [0.01, 'gray'],
                    [0.01, 'blue'],
                    [1, 'red']]
    )
]

# Build layout
layout = go.Layout(
    title='Mt Bruno Elevation',
    autosize=False,
    width=500,
    height=500,
    margin=dict(
        l=65,
        r=50,
        b=65,
        t=90
    )
)
fig = go.FigureWidget(data=data, layout=layout)
fig

newplot%20(32)

Hope that helps get you started,
-Jon

3

Hey Jon,
Thanks for the advice.
Quick question though: wouldnā€™t this solution ever so slightly shift the linear interpolation range of the colorscale so that it happens from 0.01 - 1? Even if it does, for my purposes this is fine, Iā€™m just wondering if that is whatā€™s happening.

4

Hi @gekko102,

Yes, this would shift the interpolation range a small amount. With a bit more care, it would be possible to set cmin to a value that would cause the colorscaleā€™s zero to line up exactly with the bottom of the colored region of the colorbar, in which case the coloring would be identical to the case without nanā€™s with cmin set to 0.

For the example above

cmin = 350 - 350/0.99
     = -3.5353

Hope that makes sense,
-Jon

5

I understand, youā€™re basically making ā€˜deadspaceā€™ for the 0.01 you allocated to the gray nans.
Thanks for your helpful responses Jon.

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