add expr functions for extensional selection predicates #3009
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This PR adds two new expression functions to support extensional predicates for Vega-Lite selections. This is (currently) most useful to support interval selections over cartographic projections (vega/vega-lite#6953).
An example output Vega spec for Vega-Lite geo-interval selections
{ "$schema": "https://vega.github.io/schema/vega/v5.json", "background": "white", "padding": 5, "width": 500, "height": 300, "style": "cell", "data": [ { "name": "brush_store", "transform": [ {"type": "formula", "expr": "datum.values[0]", "as": "_vgsid_"}, {"type": "collect", "sort": {"field": "_vgsid_"}} ] }, { "name": "source_0", "url": "data/us-10m.json", "format": {"type": "topojson", "feature": "states"}, "transform": [{"type": "identifier", "as": "_vgsid_"}] }, { "name": "source_1", "url": "data/airports.csv", "format": {"type": "csv", "delimiter": ","}, "transform": [ {"type": "identifier", "as": "_vgsid_"}, { "type": "geojson", "fields": ["longitude", "latitude"], "signal": "layer_1_geojson_0" }, { "type": "geopoint", "projection": "projection", "fields": ["longitude", "latitude"], "as": ["layer_1_x", "layer_1_y"] } ] } ], "projections": [ { "name": "projection", "size": {"signal": "[width, height]"}, "fit": {"signal": "[data('source_0'), layer_1_geojson_0]"}, "type": "albersUsa" } ], "signals": [ { "name": "unit", "value": {}, "on": [ {"events": "mousemove", "update": "isTuple(group()) ? group() : unit"} ] }, { "name": "brush", "update": "vlSelectionResolve(\"brush_store\", \"union\")" }, { "name": "brush_x", "value": [], "on": [ { "events": { "source": "scope", "type": "mousedown", "filter": [ "!event.item || event.item.mark.name !== \"brush_brush\"" ] }, "update": "[x(unit), x(unit)]" }, { "events": { "source": "window", "type": "mousemove", "consume": true, "between": [ { "source": "scope", "type": "mousedown", "filter": [ "!event.item || event.item.mark.name !== \"brush_brush\"" ] }, {"source": "window", "type": "mouseup"} ] }, "update": "[brush_x[0], clamp(x(unit), 0, width)]" }, { "events": [{"source": "scope", "type": "dblclick"}], "update": "[0, 0]" }, { "events": {"signal": "brush_translate_delta"}, "update": "clampRange(panLinear(brush_translate_anchor.extent_x, brush_translate_delta.x / span(brush_translate_anchor.extent_x)), 0, width)" }, { "events": {"signal": "brush_zoom_delta"}, "update": "clampRange(zoomLinear(brush_x, brush_zoom_anchor.x, brush_zoom_delta), 0, width)" } ] }, { "name": "brush_y", "value": [], "on": [ { "events": { "source": "scope", "type": "mousedown", "filter": [ "!event.item || event.item.mark.name !== \"brush_brush\"" ] }, "update": "[y(unit), y(unit)]" }, { "events": { "source": "window", "type": "mousemove", "consume": true, "between": [ { "source": "scope", "type": "mousedown", "filter": [ "!event.item || event.item.mark.name !== \"brush_brush\"" ] }, {"source": "window", "type": "mouseup"} ] }, "update": "[brush_y[0], clamp(y(unit), 0, height)]" }, { "events": [{"source": "scope", "type": "dblclick"}], "update": "[0, 0]" }, { "events": {"signal": "brush_translate_delta"}, "update": "clampRange(panLinear(brush_translate_anchor.extent_y, brush_translate_delta.y / span(brush_translate_anchor.extent_y)), 0, height)" }, { "events": {"signal": "brush_zoom_delta"}, "update": "clampRange(zoomLinear(brush_y, brush_zoom_anchor.y, brush_zoom_delta), 0, height)" } ] }, { "name": "brush_tuple", "update": "vlSelectionTuples(intersect([[brush_x[0], brush_y[0]],[brush_x[1], brush_y[1]]], {markname: \"layer_1_marks\"}, unit.mark), {unit: \"layer_1\", fields: [brush_tuple_fields[0]]})" }, { "name": "brush_tuple_fields", "value": [ {"type": "E", "field": "_vgsid_"}, {"field": "longitude", "channel": "x", "type": "E"}, {"field": "latitude", "channel": "y", "type": "E"} ] }, { "name": "brush_translate_anchor", "value": {}, "on": [ { "events": [ {"source": "scope", "type": "mousedown", "markname": "brush_brush"} ], "update": "{x: x(unit), y: y(unit), extent_x: slice(brush_x), extent_y: slice(brush_y)}" } ] }, { "name": "brush_translate_delta", "value": {}, "on": [ { "events": [ { "source": "window", "type": "mousemove", "consume": true, "between": [ { "source": "scope", "type": "mousedown", "markname": "brush_brush" }, {"source": "window", "type": "mouseup"} ] } ], "update": "{x: brush_translate_anchor.x - x(unit), y: brush_translate_anchor.y - y(unit)}" } ] }, { "name": "brush_zoom_anchor", "on": [ { "events": [ { "source": "scope", "type": "wheel", "consume": true, "markname": "brush_brush" } ], "update": "{x: x(unit), y: y(unit)}" } ] }, { "name": "brush_zoom_delta", "on": [ { "events": [ { "source": "scope", "type": "wheel", "consume": true, "markname": "brush_brush" } ], "force": true, "update": "pow(1.001, event.deltaY * pow(16, event.deltaMode))" } ] }, { "name": "brush_modify", "on": [ { "events": {"signal": "brush_tuple"}, "update": "modify(\"brush_store\", brush_tuple, true)" } ] } ], "marks": [ { "name": "brush_brush_bg", "type": "rect", "clip": true, "encode": { "enter": {"fill": {"value": "#333"}, "fillOpacity": {"value": 0.125}}, "update": { "x": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_x[0]" }, {"value": 0} ], "y": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_y[0]" }, {"value": 0} ], "x2": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_x[1]" }, {"value": 0} ], "y2": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_y[1]" }, {"value": 0} ] } } }, { "name": "layer_0_marks", "type": "shape", "style": ["geoshape"], "interactive": false, "from": {"data": "source_0"}, "encode": { "update": { "fill": {"value": "lightgray"}, "stroke": {"value": "white"}, "ariaRoleDescription": {"value": "geoshape"} } }, "transform": [{"type": "geoshape", "projection": "projection"}] }, { "name": "layer_1_marks", "type": "symbol", "style": ["circle"], "interactive": true, "from": {"data": "source_1"}, "encode": { "update": { "opacity": {"value": 0.7}, "fill": [ { "test": "!(length(data(\"brush_store\"))) || (vlSelectionIdTest(\"brush_store\", datum))", "value": "red" }, {"value": "steelblue"} ], "ariaRoleDescription": {"value": "circle"}, "description": { "signal": "\"longitude: \" + (format(datum[\"longitude\"], \"\")) + \"; latitude: \" + (format(datum[\"latitude\"], \"\"))" }, "x": {"field": "layer_1_x"}, "y": {"field": "layer_1_y"}, "size": {"value": 10}, "shape": {"value": "circle"} } } }, { "name": "brush_brush", "type": "rect", "clip": true, "encode": { "enter": {"fill": {"value": "transparent"}}, "update": { "x": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_x[0]" }, {"value": 0} ], "y": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_y[0]" }, {"value": 0} ], "x2": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_x[1]" }, {"value": 0} ], "y2": [ { "test": "data(\"brush_store\").length && data(\"brush_store\")[0].unit === \"layer_1\"", "signal": "brush_y[1]" }, {"value": 0} ], "stroke": [ { "test": "brush_x[0] !== brush_x[1] && brush_y[0] !== brush_y[1]", "value": "white" }, {"value": null} ] } } } ] }For the spec above, I'll call out the specific places these new functions are being used:
intersectfunction) to selection tuples:{ "name": "brush_tuple", "update": "vlSelectionTuples(intersect([[brush_x[0], brush_y[0]],[brush_x[1], brush_y[1]]], {markname: \"layer_1_marks\"}, unit.mark), {unit: \"layer_1\", fields: [brush_tuple_fields[0]]})" }vlSelectionIdTestto do a binary search over this dataset:{ "name": "layer_1_marks", "type": "symbol", "style": ["circle"], "interactive": true, "from": {"data": "source_1"}, "encode": { "update": { "opacity": {"value": 0.7}, "fill": [ { "test": "!(length(data(\"brush_store\"))) || (vlSelectionIdTest(\"brush_store\", datum))", "value": "red" }, {"value": "steelblue"} ]