Update mark.md to include ranged marks.

[kanitw]

We haven't shown how to use x2 and y2 at all

[kanitw]

Step 1. Create examples for different ranged mark types

• bar/rule
  • replicate https://vega.github.io/vega/examples/timelines/?
  • replicate error bar with rule similar to https://vega.github.io/vega/examples/error-bars/? (Just do confidence interval is fine)
• area
  • use ranged area to show confidence interval of line charts akin to last example in http://ggplot2.tidyverse.org/reference/geom_ribbon.html (You will have a find a good data yourself

(You can submit one or more example at a time -- whichever you think makes it easier for us to review.)

Step 2. Add them to different parts of marks.md with description paragraphs

[ayush29feb]

Ran into some issues while recreating the https://vega.github.io/vega/examples/timelines/ example.

• vega-lite doesn't allow multiple data sources so I couldn't figure out how to load both presidents and events described in the vega doc. Maybe I misunderstood but this was presented in Support multiple source datasets like vega #1271
• the sort property of the mark wasn't working. I made a separate issue for that Sort Property of Mark Not Working #2533

Another small thing, the size property isn't documented for rules mark in the docs. Maybe we should include it.

Here is what I got so far.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": {
    "name": "people",
    "values": [
      {
        "label": "Washington",
        "born": -7506057600000,
        "died": -5366196000000,
        "enter": -5701424400000,
        "leave": -5453884800000
      }
      ...
    ]
  },
  "layer": [
    {
      "mark": "rule",
      "encoding": {
        "x": {
          "field": "born",
          "type": "temporal",
          "timeUnit": "year",
          "axis": {"title": "Year"}
        },
        "x2": {
          "field": "died",
          "type": "temporal",
          "timeUnit": "year"
        },
        "y": {
          "field": "label",
          "type": "nominal",
          "axis": {"title": "President"}
        },
        "color": {"value": "black"},
        "size": {"value": 2}
      }
    },
    {
      "mark": "rule",
      "encoding": {
        "x": {
          "field": "enter",
          "type": "temporal",
          "timeUnit": "year"
        },
        "x2": {
          "field": "leave",
          "type": "temporal",
          "timeUnit": "year"
        },
        "size": {"value": 4},
        "y": {
          "field": "label",
          "type": "nominal"
        },
        "color": {"value": "red"}
      }
    }
  ]
}

[ayush29feb]

For the confidence intervals, do we have a aggregate function to calculate the 95% value? I am currently plotting q1 and q3

[ayush29feb]

For the ranged area chart, is this example not good enough?
http://www.ayush.xyz/vega-editor-demo/?mode=vega-lite&spec=confidence_interval

(same issue, do we have a aggregate function to calculate 95%?)

[domoritz]

vega-lite doesn't allow multiple data sources so I couldn't figure out how to load both presidents and events described in the vega doc

Use layers or lookup

[domoritz]

Another small thing, the size property isn't documented for rules mark in the docs. Maybe we should include it.

Please send a separate PR!

[kanitw]

For the confidence intervals, do we have a aggregate function to calculate the 95% value? I am currently plotting q1 and q3

They are called ci0 and ci1 -- I believe. (See Vega docs and if Vega-Lite docs do not have them, please help update accordingly.) :)

[kanitw]

Consolidated as a part of #2854.