add_hline and add_vline (+add_vrect/add_hrect)

[nicolaskruchten]

We should add these convenience methods, as the ref=x/ref=paper trick is pretty hard for people to understand.

We'd want to be able to add these to all subplots, one subplot, or possibly a single row or a single column. Moved to #2140

We'd also want add_vspan and add_hspan (or vrect/hrect, not set on the names)

[emmanuelle]

Also requested in https://community.plot.ly/t/speeding-up-fig-add-shape-calls-in-python/35880/2

[nicolaskruchten]

Related to #2140

[jvschoen]

A quick solution would be:

fig.layout.update(shapes=[{'type': 'line','y0':y_intercept,'y1': y_intercept,
                           'x0':str(df.x_value.min()), 'x1':str(df.x_value.max()),
                           'xref':'x' + str(i + 1), 'yref':'y' + str(i + 1),
                           'line': {'color': 'black', 'width': 1, 'dash': 'dot'}} 
                          for i, member in enumerate(pd.unique(df.x_value))])

[jvschoen]

Though an issue arrises if you want to add both an x and y line, the second update will overwrite the former and you only see the last added line. As a workaround for that :

list(np.array([ 
        [
        # Horizontal Line
        {'type': 'line',
         'y0': df.y_val.min(),'y1': df_faces.y_val.max(),
         'x0': df.x_val.median(), 'x1': df.x_val.median(),
         'xref':'x' + str(i + 1),
         'yref':'y' + str(i + 1),
         'line': {'color': 'black','width': 1, 'dash': 'dot'}},
        # Vertical Line
        {'type': 'line',
         'y0': df.y_val.median(),'y1': df..median(),
         'x0':str(df.x_val.min()), 'x1':str(df.x_val.max()),
         'xref':'x' + str(i+1),
         'yref':'y' + str(i + 1),
         'line': {'color': 'black','width': 1, 'dash': 'dot'}}
        ]
        for i , member in enumerate(pd.unique(df.facets_val))]).ravel())

So now I see why you referred to this current usage as a bit clunky

[nicolaskruchten]

Well we have fig.add_shape() already that doesn't overwrite :)

But what I'm hoping for is a way to have a single function call fig.add_hline(5) which will add a line at y=5 to all subplots, and then some options like fig.add_hline(5, row=1, col=2) for individual subplots :)

[MrPaulAR]

I would also ask that you consider the ability to add text to the upcoming "add_hline" and "add_vline" items.

[anuraghuram]

There should also be an option to resize v/h lines to fit the plot's min and max y/x axis respectively. I notice that when I add a vline over an existing plot, it runs off the plot (as I presume is happening in the screenshots provided in this thread plotly/plotly_express#143)

[nicolaskruchten]

@nicholas-esterer let's start with this issue for now, without tackling the "all subplots" or "one row of subplots" just yet. Let's do the easy case to get going. cc @emmanuelle

[nicolaskruchten]

Let's do the "hard version" with the multi-subplot targeting as part of #2140