bar base attribute doesn't work on date axis

[cldougl]

Using the base attribute with date data creates an incorrect range and doesn't apply base correctly: https://codepen.io/plotly/pen/JpvajW

[alexcjohnson]

Hmm yeah, we definitely shouldn't do what we're doing now (which it appears is converting to ms since 1970 and adding that on to the base date) but I don't think what you're expecting is consistent with how base works on other axis types. y is supposed to be the size of the bar, and base is where it starts. I suppose we could do either or both of:

• Allow specifying y in milliseconds, and use base to determine the axis type - this almost works right now with explicit axis type, though it seems we make a timezone error - see https://codepen.io/alexcjohnson/pen/eVrPyr
• Make a new attribute like end (what's the other end called if the start is base?) to use instead of y to use when you want to specify absolute values for both ends of the bar rather than base+delta

[cldougl]

got it -- you're right, I was expecting y to be treated as an 'end' rather than a 'delta'. In that case I think:

Allow specifying y in milliseconds, and use base to determine the axis type - this almost works right now with explicit axis type, though it seems we make a timezone error - see https://codepen.io/alexcjohnson/pen/eVrPyr

is a good method to document.

For the second option of adding an attribute, it might be an option to add a mode instead of a new array attribute where ymode: 'delta' | 'end'. This option would be useful for users creating gantt type charts.

[FrankWessels]

Here another example of a problem caused by this issue:

https://codepen.io/etpinard/pen/MGdRKq?editors=1010

Might be helpful when solving? Note that when not specifying the xaxis type in this example, the graph is the same for everyone, no matter the timezone.

[etpinard]

y is supposed to be the size of the bar, and base is where it starts.

On a similar topic, what should base do on category size axes? Right now,

Plotly.newPlot('graph', [{
  type: 'bar',
  x: ['a', 'b', 'c'],
  base: -0.5
}])

it is completely off:

swapping d2c for d2l_noadd for category (and multicategory) axes here:

https://github.com/plotly/plotly.js/blob/7bb5daaaa118537ca01464d12cdbcef6f9cc764a/src/traces/bar/cross_trace_calc.js#L131

and

https://github.com/plotly/plotly.js/blob/7bb5daaaa118537ca01464d12cdbcef6f9cc764a/src/traces/bar/cross_trace_calc.js#L142

gives "better" results:

but still doesn't look right.

[alexcjohnson]

but still doesn't look right.

What would be "right"? Is there a use case here or should we just prohibit base+(multi)category during supplyDefaults?

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson

[jpjsonic]

@gvwilson I think this is still a pretty significant issue that's worth looking at. Fixing this unlocks really powerful charts like Gantt plots. Here's an example of a Gantt plot that I was trying to make:

const projectsData = [
    { project: "Website Speed", start_date: "2024-02-14", finish_date: "2024-03-07" },
    { project: "Database Migration", start_date: "2024-02-22", finish_date: "2024-03-05" },
    { project: "Bug Fix", start_date: "2024-02-12", finish_date: "2024-02-18" }
];

const trace = {
    type: 'bar',
    x: projectsData.map(d => d.finish_date),
    y: projectsData.map(d => d.project),
    orientation: 'h',
    base: projectsData.map(d => d.start_date)
};

const layout = {
    title: {
        text: 'Project Duration Gantt Chart<br><sub>Visualizing the duration of each project over time</sub>',
    },
    xaxis: {
        type: 'date',
    },
    yaxis: {
    margin: {
        l: 130
    }
};

Plotly.newPlot('chart', [trace], layout);

If you leave the base in the chart you get really odd benavior on the xaxis just as everyone has said above: However, just commenting out the base the axis works again as expected, but of course is lacking a bar start date:

[jpjsonic]

@gvwilson Is it possible for us to re-open this issue?