Share colormap for plotly stacked heatmaps

When working with stacked heatmaps in Plotly, it can be useful to share the colormap across all the subplots. This allows for easier comparison between the different heatmaps. In this article, we will explore three different ways to achieve this in Julia.

Option 1: Using the `colorscale` parameter

One way to share the colormap is by specifying the `colorscale` parameter when creating the heatmaps. This parameter allows you to define a custom colormap that will be used for all the subplots. Here’s an example:


using PlotlyJS

# Define the custom colormap
colorscale = [
    [0, "rgb(255, 0, 0)"],
    [0.5, "rgb(0, 255, 0)"],
    [1, "rgb(0, 0, 255)"]
]

# Create the first heatmap
heatmap1 = heatmap(z = rand(5, 5), colorscale = colorscale)

# Create the second heatmap
heatmap2 = heatmap(z = rand(5, 5), colorscale = colorscale)

# Create the stacked heatmaps
layout = Layout(grid = Dict(:rows => 2, :columns => 1))
plot([heatmap1, heatmap2], layout)

This approach allows you to have full control over the colormap used in the heatmaps. However, it can be cumbersome if you have a large number of subplots or if you want to use a predefined colormap.

Option 2: Using the `colorway` parameter

Another way to share the colormap is by specifying the `colorway` parameter when creating the heatmaps. This parameter allows you to define a list of colors that will be used cyclically for the subplots. Here’s an example:


using PlotlyJS

# Define the list of colors
colorway = ["rgb(255, 0, 0)", "rgb(0, 255, 0)", "rgb(0, 0, 255)"]

# Create the first heatmap
heatmap1 = heatmap(z = rand(5, 5), colorway = colorway)

# Create the second heatmap
heatmap2 = heatmap(z = rand(5, 5), colorway = colorway)

# Create the stacked heatmaps
layout = Layout(grid = Dict(:rows => 2, :columns => 1))
plot([heatmap1, heatmap2], layout)

This approach is simpler than the previous one, as it allows you to specify a list of colors instead of a full colormap. However, it may not provide as much control over the colormap as the previous option.

Option 3: Using a shared `coloraxis`

A third way to share the colormap is by using a shared `coloraxis` object. This allows you to define a single colormap that will be used for all the subplots. Here’s an example:


using PlotlyJS

# Create the first heatmap
heatmap1 = heatmap(z = rand(5, 5))

# Create the second heatmap
heatmap2 = heatmap(z = rand(5, 5))

# Create the stacked heatmaps
layout = Layout(grid = Dict(:rows => 2, :columns => 1))
layout[:coloraxis] = Dict(:colorscale => "Viridis")
plot([heatmap1, heatmap2], layout)

This approach is the simplest of the three, as it allows you to use a predefined colormap without having to specify individual colors or scales. However, it may not provide as much flexibility as the previous options.

In conclusion, the best option depends on your specific requirements. If you need full control over the colormap, option 1 is the way to go. If simplicity is more important, option 3 is a good choice. Option 2 provides a balance between control and simplicity. Choose the option that best suits your needs and preferences.

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