`add_trace` with `type = 'scatter', mode = 'lines'` works differently from `add_lines`

When plotting a regression line with confidence intervals, add_trace with type = 'scatter', mode = 'lines' works differently from add_lines. The latter works while the former fails (see examples).

Looks like add_trace(type = 'scatter', mode = 'lines', ...) attempts to connect datapoints pairwise instead of sequentially.

# load packages
require(dplyr)
require(plotly)

# prep data 
setosa <- iris |> 
  filter(Species == "setosa") |> 
  mutate(fit = predict(lm(Sepal.Width ~ Sepal.Length), interval = "conf")[, "fit"],
         lwr = predict(lm(Sepal.Width ~ Sepal.Length), interval = "conf")[, "lwr"],
         upr = predict(lm(Sepal.Width ~ Sepal.Length), interval = "conf")[, "upr"])

## Compare plots ##

# plot 1: add_lines works
plot_ly(data = setosa, x = ~Sepal.Length) |> 
  add_trace(y = ~Sepal.Width,
            type = 'scatter',
            mode = 'markers',
            showlegend = FALSE) |>
  add_lines(y = ~upr, # add_lines works
            color = I("#2ca02c"),
            name = 'CI upper') |> 
  add_lines(y = ~lwr, # add_lines works
            color = I("#2ca02c"),
            alpha = 0.2,
            fill = 'tonexty',
            name = 'CI lower') |> 
  add_trace(y = ~fit, # add_trace works
            type = 'scatter',
            mode = 'lines', 
            name = 'Predicted')

# plot 2: replaced add_lines with add_trace, no other changes
plot_ly(data = setosa, x = ~Sepal.Length) |> 
  add_trace(y = ~Sepal.Width,
            type = 'scatter',
            mode = 'markers',
            showlegend = FALSE) |>
  add_trace(y = ~upr, # add_trace doesn't work
            type = 'scatter',
            mode = 'lines',
            color = I("#2ca02c"),
            name = 'CI upper') |> 
  add_trace(y = ~lwr, # add_trace doesn't work
            type = 'scatter',
            mode = 'lines',
            color = I("#2ca02c"),
            alpha = 0.2,
            fill = 'tonexty',
            name = 'CI lower') |> 
  add_trace(y = ~fit, # here add_trace works as it should
            type = 'scatter',
            mode = 'lines', 
            name = 'Predicted')

Output

Plot 1:

Plot 2:

R plotting API の add_trace と add_lines のエントリポイントから始め、提供された iris 回帰例を再現します。2 つの関数が mode = 'lines' の散布トレースをどのように処理するかを比較し、その後、add_lines を add_trace に置き換えると同じ連続的な信頼区間の線と塗りつぶしが生成されることを確認します。