Customize value labels for lower/upper in range charts

[kentcb]

Description

Labels for lower/upper values are based on Ticktext except when they don't align perfectly, in which case there does not appear to be a way to customize the labels (they instead show raw values).

Repro steps

let yAxis =
    Axis.LinearAxis.init(
        Title = "Y",
        Showline = true,
        Range = StyleParam.Range.MinMax (0.0, 2.0),
        Tickvals = [0.0 .. 2.0],
        Ticktext = [ "zero"; "one"; "two" ]
    )
Chart.Range(
    [1;2],
    [1;1],
    [0.0;0.53622183],
    [1.0;2.0],
    StyleParam.Mode.None,
    Name = "",
    LowerName = "Lower",
    UpperName = "Upper",
    Labels = [])
|> Chart.withY_Axis (yAxis)
|> Chart.Show

This looks fine when hovering over values that align perfectly with tick increments:

But when hovering over misaligned values, one sees the raw value:

Expected behavior

A means of providing labels for both upper and lower. In my case, I'm mapping values to times, so when it aligns perfectly I see a time of day, but when it doesn't I see an ugly floating point value.

Actual behavior

As far as I can tell, there's no API for this.

Known workarounds

None.

Related information

• Windows 10
• 2.0.0-preview.1
• .NET 5

[kMutagene]

I think this is definitely a meaningful addition to the range chart, i will add LowerLabels and UpperLabels to the method.

Two suggestions from my side in the meantime:

1. You seem to be very interested in Range Charts - in your case it might be in the long run worth it to compose the Chart yourself (it is three line charts for upper, mean and lower values, with a Fill=StyleParam.Fill.ToNext_y for the upper trace). That way you have full control over all three traces, and the argument list of this function stays manageable - I do not think that it is good to get all possible styling arguments of Line traces for all three subtraces of the range chart into the Chart.Range method, it would be quite an amount of arguments.

2. Another approach for full control would be customizing each trace via the genericChart.mapiTrace function, customizing each trace after you used the Chart.Range method:

Chart.Range(
    [1;2],
    [1;1],
    [0.0;0.53622183],
    [1.0;2.0],
    StyleParam.Mode.None,
    Name = "",
    LowerName = "Lower",
    UpperName = "Upper",
    Labels = [])
|> Chart.withY_Axis (yAxis)
|> GenericChart.mapiTrace (fun i t ->
    match i with
    | 0 -> t |> Trace.TraceStyle.TextLabel ["upperOne";"upperTwo"]
    | 1 -> t |> Trace.TraceStyle.TextLabel ["lowerOne";"lowerTwo"]
    | 2 -> t
)
|> Chart.Show

Not sure if you want to get rid of the value display above the label as well though.

[kentcb]

Haha, I was just looking at this again and came back to post my (ugly) solution. I also added LowerLabels and UpperLabels to Chart.Range with an intent to PR, but then found I also needed control over the template and went down the dynamic route. However, I wasn't aware of mapiTrace, so I ended up with this monstrosity:

let yAxis =
    Axis.LinearAxis.init(
        Title = "Y",
        Showline = true,
        Range = StyleParam.Range.MinMax (0.0, 2.0),
        Tickvals = [0.0 .. 2.0],
        Ticktext = [ "zero"; "one"; "two" ]
    )

Chart.Range(
    [1;2],
    [1;1],
    [1.0;2.0],
    [0.0;0.53622183],
    StyleParam.Mode.None,
    Name = "",
    LowerName = "Lower",
    //LowerLabels = ["nada";"around one half"],
    UpperName = "Upper",
    //UpperLabels = ["one";"Two!"],
    Labels = [])
|> Chart.withY_Axis (yAxis)
|> (fun chart ->
        match chart with
        | GenericChart.MultiChart ([lower;upper;_], _, _, _) ->
            lower?text <- ["nada";"around one half"]
            lower?hovertemplate <- "%{text}"

            upper?text <- ["one";"Two!"]
            upper?hovertemplate <- "%{text}"

            chart
        | _ -> failwith "Couldn't set dynamic options")
|> Chart.Show

[kMutagene]

As long as it worked out for you and you found where to customize things, i would count that as a win generally 😄. I added LowerLabels and UpperLabels to Chart.Range, so you do not have to do this in the future though ;) the package (2.0.0-preview.4) should be up on nuget any minute