vega-lite: plotting a column name with '.' in it eventually leads to a vega error

I’m doing an Altair chart with a color given by color=Color('gpuinfo.name:N', .... This produces an eventual Vega error.

(Why do I have a column with a period in its name? Reading nested JSONs into pandas is nicely handled by json_normalize, which flattens nested JSON levels into dot-separated column names.)

undefined:3
return x["gpuinfo"]["name"];
                   ^

TypeError: Cannot read property 'name' of undefined
    at Object.eval [as get] (eval at <anonymous> (/Users/jowens/Documents/working/vega/node_modules/datalib/src/util.js:147:20), <anonymous>:3:20)
    at Facetor.proto._cellkey (/Users/jowens/Documents/working/vega/node_modules/datalib/src/aggregate/aggregator.js:106:23)
    at Facetor.proto._cell (/Users/jowens/Documents/working/vega/node_modules/datalib/src/aggregate/aggregator.js:114:38)
    at Facetor.proto._add (/Users/jowens/Documents/working/vega/node_modules/datalib/src/aggregate/aggregator.js:151:19)
    at add (/Users/jowens/Documents/working/vega/src/transforms/Aggregate.js:174:31)
    at Array.forEach (native)
    at Aggregate.prototype.transform (/Users/jowens/Documents/working/vega/src/transforms/Aggregate.js:190:13)
    at Aggregate.prototype.evaluate (/Users/jowens/Documents/working/vega/src/transforms/Transform.js:48:15)
    at Node.dataRef (/Users/jowens/Documents/working/vega/src/scene/Scale.js:387:15)
    at Node.ordinal (/Users/jowens/Documents/working/vega/src/scene/Scale.js:127:20)

About this issue

Original URL
State: closed
Created 8 years ago
Comments: 17 (9 by maintainers)

Most upvoted comments

I found some related issues in Vega 3, and just published an updated version of vega-util that resolves them. By default, Vega will try to parse field names like "a.a" into nested lookups (datum['a']['a']). However, you can indicate non-nested field names by wrapping the name in brackets. For example, the field names [a.a] and ['a.a'] will both map to datum['a.a']. It is also legal to use escape characters: a\\.a -> datum['a.a'].

If you are referring to such fields within an expression, simply use standard JavaScript bracket notation: datum['a.a'].

Vega-Lite probably needs to perform a check to see if the . character is in the field name, and if so, wrap the field name in brackets.

jheer on Jan 25, 2017

@willium this toy spec should (WIP) work:

{
  "description": "A simple bar chart with embedded data.",
  "data": {
    "values": [
      {"a.a": "A","b": 28}, {"a.a": "B","b": 55}
    ]
  },
  "mark": "bar",
  "encoding": {
    "x": {"field": "a.a", "type": "ordinal"},
    "y": {"field": "b", "type": "quantitative"}
  }
}

@jowens still doesn’t work. For debugging purpose.

kanitw on Jan 25, 2017