[add] stacked area chart example

[extua]

Added a short example for creating a stacked area chart.

[Mc-Zen]

This is a great idea, especially until there is a built-in function for that. Also see lilaq-project/lilaq#105.

I wonder whether it is more useful for users to provide the solution for any number of series (given in the first answer to the issue linked above). Also, the example does not compile at the moment because the x array is not defined.

[extua]

I didn't see your example in lilaq-project/lilaq#105 (comment); the way you've written it is much better!

[Mc-Zen]

How about we propose an implementation of a new high-level plot type stacked-area like this

#let stacked-area(x, ..y) = {
  y
    .pos()
    .fold(
      ((0,) * x.len(),) , (ys-stacked, ys) => {
        let previous = ys-stacked.last()
        ys-stacked.push(lq.vec.add(previous, ys))
        ys-stacked
      }
    )
    .windows(2)
    .map(((y1, y2)) => lq.fill-between(x, y1, y2: y2))
}

#let x = range(10)
#let y1= (0, 1, 3, 9, 5, 4, 2, 2, 1, 0)
#let y2 = (5, 3, 2, 0, 1, 2, 2, 2, 3, 2)
#let y3 = (0, 0, 0, 0, 1, 2, 4, 5, 5, 9)

#lq.diagram(
  ..stacked-area(x, y1, y2, y3)
)

The user can check out and see how stacked-area works. but does not need to touch it in order to use it. I feel like this is a nice solution until this is built in.

[extua]

How about we propose an implementation of a new high-level plot type stacked-area like this

I agree, what do you think of this -- dfa2788

[Mc-Zen]

Nice. Thank you for this good idea and contribution!