The short answer is there is no way to make the dropdown options refer to a data field. So let's look at the long answer.

Here's my issue. I have a table of names. I want to display those names in a dropdown for the user to select one of them. Then I want to filter some data based on the selected value. So I'd love to do something like this:

{
"\$schema": "https://vega.github.io/schema/vega/v5.json",
"title": "GPU Benchmarks",
"width": 1400,
"height": 1300,
"signals": [
{
"name": "selected_game",
"bind": {
"input": "select",
"options": {"data": "games", "field": "name"}
}
}
],
"data": [
{
"name": "games",
"url": "some url..."
}, {
"name": "data_to_filter",
"transform": [{
"type": "filter",
filter based on selected_game
}]
"url": "some other url"
}
],
...


This feature is missing from Vega, and there were feature requests filed:

Another option is to generate the input ourself in the HTML, then bind it to Vega. See the doc.

A final option is to simply generate the whole list of options somewhere else, and put it directly in the list of bound options. I went with that:

  "signals": [
{
"name": "selected_game",
"bind": {
"input": "select",
"options": ["game1", "game2", ...]
}
}
],
"data": [
{
"name": "game_benchmarks",
"url": "some url",
"transform": [
{ "type": "filter", "expr": "datum.name == game_name" }
]
}
]
...