plotly sankey graph data formatting

Question

plotly library has some nice sankey diagrams https://plotly.com/python/sankey-diagram/

but the data requires you to pass indexes of the source/target pairs.

    link = dict(
      source = [0, 1, 0, 2, 3, 3], # indices correspond to labels, eg A1, A2, A1, B1, ...
      target = [2, 3, 3, 4, 4, 5],

I was wondering if there's an API to simply pass a named list of these pairs?

links = [
    {'source': 'start', 'target': 'A', 'value': 2},
    {'source': 'A', 'target': 'B', 'value': 2},
...
]

this is more inline with how bokeh/holoviews expects data (but that sankey doesn't work with self-loops)

and also this pysankey widget

so i can closer map to my dataframe without processing everything?

or, is there a nice pythonic way to convert this in a one liner :D

Answer 1

• the structure is clearly a pandas dataframe constructor format
• create a dataframe from it, plus the key series of the nodes
• from this it's simple to construct a Sankey plot from it

import pandas as pd
import numpy as np
import plotly.graph_objects as go

links = [
    {'source': 'start', 'target': 'A', 'value': 2},
    {'source': 'A', 'target': 'B', 'value': 1},
    {'source': 'A', 'target':'C', 'value':.5}

]

df = pd.DataFrame(links)
nodes = np.unique(df[["source","target"]], axis=None)
nodes = pd.Series(index=nodes, data=range(len(nodes)))

go.Figure(
    go.Sankey(
        node={"label": nodes.index},
        link={
            "source": nodes.loc[df["source"]],
            "target": nodes.loc[df["target"]],
            "value": df["value"],
        },
    )
)