Adding a filter or changing encoding type causes Error: Arrow field values can not be overwritten.

[tjader]

Hi, It looks like the arrow loader fails if the chart is having some transforms (at least the filter transform) or if the field type is changed in the encoding. The error thrown is Error: Arrow field values can not be overwritten.

It seems that the vega library is in many cases writing back into the object in-place, even though the in-place writing seems write back the same data.
Commenting out the line throwing the error made the figures render, but I'm not sure it is a good solution moving forward.

        set: function() {
          //throw Error('Arrow field values can not be overwritten.');  <--commented out line
        },
        enumerable: true
      });
   ...

This baseline chart works out of the box (using the current master of vega-loader-arrow)

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "url": "https://gist.githubusercontent.com/domoritz/0f53a5abde95564c36dfaac623a7a922/raw/cce3719b853e25d5dfff97a270283ba83af3c0e6/flights-10k.arrow",
    "format": {
      "type": "arrow"
    }
  },
  "encoding": {
    "x": {
      "field": "FL_DATE"
    },
    "y": {
      "aggregate": "sum",
      "field": "ARR_DELAY",
      "type": "quantitative"
    }
  },
  "mark": {
    "type": "bar"
  }
}

But adding a filter causes the error.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "url": "https://gist.githubusercontent.com/domoritz/0f53a5abde95564c36dfaac623a7a922/raw/cce3719b853e25d5dfff97a270283ba83af3c0e6/flights-10k.arrow",
    "format": {
      "type": "arrow"
    }
  },
  "transform": [
    { "filter": {
      "field": "ARR_DELAY",
      "gt": 360.0
    }}
    ],
  "encoding": {
    "x": {
      "field": "FL_DATE"
    },
    "y": {
      "aggregate": "sum",
      "field": "ARR_DELAY",
      "type": "quantitative"
    }
  },
  "mark": {
    "type": "bar"
  }
}

I have attached a few other examples of failing renders. They all work if the exception is commented out.
[flight10k_filter.json](https://github.com/vega/vega-loader-arrow/files/13818262/flight10k_filter.json)
[flight10k_ordinal.json](https://github.com/vega/vega-loader-arrow/files/13818263/flight10k_ordinal.json)
[flight10k_timeunit.json](https://github.com/vega/vega-loader-arrow/files/13818264/flight10k_timeunit.json)
[flight10k_temporal.json](https://github.com/vega/vega-loader-arrow/files/13818265/flight10k_temporal.json)
[flight10k_ok.json](https://github.com/vega/vega-loader-arrow/files/13818267/flight10k_ok.json)

I have tested these against the latest master (the latest release 0.1.0 uses arrow 6 which is not compatible with the dataset), where I also could confirm the "fix" of removing raising the error.

Btw, it would be nice to have a new release with a more up-to-date version of arrow supported.

[domoritz]

I made a release for [email protected].

The error is coming from

vega-loader-arrow/src/arrow.js

Line 44 in 27be2c1

throw Error('Arrow field values can not be overwritten.');

as you said. Writing back to arrow shouldn't really be happening. I'd suggest finding out why the set is happening by putting a breakpoint I the code.