relating the index of fig.data to row and col

I am trying to plot a diagonal line per facet where each facet has its own axes scales.
fig.data can get me the proper range per facet via

for i, d in enumerate(fig.data):
    x0, x1= d.x.min(), d.x.max()

If I would had known the right row and col of each facet i, I would then use:
fig.add_shape(type='line',x0=x0, x1=x1, y0=x0, y1=x1, row=row, col=col)

However, to relate the index in data to the row and col needed to plot the new line is a kind of nightmare.
I tried a lot of stuff including fig._grid_ref but still no success.

help please !

[nicolaskruchten]

row and col are shortcuts to setting xref and yref on the underlying shape object. If you want to add a shape per trace, you can manually set xref and yref to match the trace's xaxis and yaxis, respectively:

import plotly.express as px

df = px.data.tips()

fig = px.scatter(df, x="total_bill", y="tip", facet_col="day", facet_col_wrap=2)
for trace in fig.data:
    fig.add_shape(
        type="line",
        x0=trace.x.min(), 
        x1=trace.x.max(), 
        y0=trace.y.min(), 
        y1=trace.y.max(),
        xref=trace.xaxis,
        yref=trace.yaxis
    )
fig.show()

Thanks @nicolaskruchten !
I want to make the plots square and equal scaled.
How does this generalize to update_xaxes? It does not get as input the xref nor yref as input.

[nicolaskruchten]

Something like this? I'm not sure how your previous question relates to your current one :)

import plotly.express as px

df = px.data.tips()

fig = px.scatter(df, x="total_bill", y="tip", facet_col="day", facet_col_wrap=2)
fig.update_xaxes(constrain="domain", range=[0,60])
fig.update_yaxes(constrain="domain", scaleratio=1, scaleanchor="x", range=[0,60])
fig.show()

I guess I have not explained myself well.
I would like different ranges per facet (subplot).
However, the update_xaxes does not get xref as argument. only col and row.

Signature:
fig.update_xaxes(
    patch=None,
    selector=None,
    overwrite=False,
    row=None,
    col=None,
    **kwargs,
)

[nicolaskruchten]

Are you manually computing the ranges or do you want them to be automatically computed? Are you creating your figure using a plotly.express method or using make_subplots ?

I use plotly.express. I am manually computing the ranges. I guess I want to do something very like your first answer but also change axes on top of plotting a line. You have suggested to pass xref=trace.xaxis, yref=trace.yaxis to fig.add_shape. I want to do something similar but to fig.update_xaxes

[nicolaskruchten]

OK, so your first step is probably to unmatch the axes:

fig.update_xaxes(matches=None)
fig.update_yaxes(matches=None)

Then it'll be a bit gross, but to update the xN axis, you can pass selector=(N-1) to fig.update_xaxes() to set its range and anchor.

[gvwilson]

Hi - we are trying to tidy up the stale issues and PRs in Plotly's public repositories so that we can focus on things that are still important to our community. Since this one has been sitting for several years, I'm going to close it; if it is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. Thanks for your help - @gvwilson