本文档介绍了如何使用 Vega 可视化语法，在力导向图中实现节点悬停时高亮显示相关链接的功能。我们将通过修改 Vega 的配置，添加交互信号和条件样式，使得当鼠标悬停在节点上时，与其相连的链接能够突出显示，从而增强数据的可探索性和可视化效果。
以下步骤将指导你如何在现有的 Vega 力导向图配置中添加节点悬停高亮链接的功能。
首先，我们需要定义一个信号来跟踪当前鼠标悬停的节点。该信号将存储悬停节点的 name 属性，并在鼠标移出节点时重置为 null。
{
"name": "active",
"value": null,
"on": [
{"events": "symbol:mouseover", "update": "datum.name"},
{"events": "mouseover[!event.item]", "update": "null"}
]
}这段代码定义了一个名为 active 的信号。它监听 symbol:mouseover 事件，当鼠标悬停在节点上时，将节点的 name 属性更新到 active 信号中。同时，它还监听 mouseover[!event.item] 事件，该事件在鼠标移出节点时触发，将 active 信号重置为 null。
为了在视觉上突出显示悬停的节点，我们可以修改节点的填充颜色。当节点的 name 属性与 active 信号的值相等时，将节点填充为黄色，否则使用默认的颜色。
"encode": {
"enter": {"stroke": {"value": "white"}},
"update": {
"fill": {
"signal": "datum.name==active?'yellow': scale('color', datum.group)"
},
"size": {"signal": "2 * nodeRadius * nodeRadius"},
"cursor": {"value": "pointer"}
}
}这段代码修改了节点 (nodes) 的 update 编码。fill 属性现在使用一个条件表达式。如果节点的 name 属性等于 active 信号的值，则填充颜色为黄色 ('yellow')；否则，使用 scale('color', datum.group) 根据节点所属的组设置颜色。
接下来，我们需要修改链接的样式，以便在节点悬停时突出显示与其相连的链接。我们可以通过检查链接的 source 或 target 是否与 active 信号的值相等来实现。
{
"type": "path",
"from": {"data": "link-data"},
"interactive": false,
"encode": {
"update": {
"stroke": {"value": "#ccc"},
"strokeWidth": {"value": 0.5}
}
},
"transform": [
{
"type": "linkpath",
"require": {"signal": "force"},
"shape": "line",
"sourceX": "datum.source.x",
"sourceY": "datum.source.y",
"targetX": "datum.target.x",
"targetY": "datum.target.y"
}
]
}这段代码定义了链接 (path) 的样式。目前，链接的颜色 (stroke) 设置为 #ccc，宽度 (strokeWidth) 设置为 0.5。要实现高亮效果，我们需要修改 update 编码，添加条件判断。由于原始问题和答案中未提供高亮链接的具体实现，以下提供一种修改思路，但需要根据实际数据结构调整：
{
"type": "path",
"from": {"data": "link-data"},
"interactive": false,
"encode": {
"update": {
"stroke": [
{
"test": "active && (datum.source.name === active || datum.target.name === active)",
"value": "red"
},
{"value": "#ccc"}
],
"strokeWidth": [
{
"test": "active && (datum.source.name === active || datum.target.name === active)",
"value": 2
},
{"value": 0.5}
]
}
},
"transform": [
{
"type": "linkpath",
"require": {"signal": "force"},
"shape": "line",
"sourceX": "datum.source.x",
"sourceY": "datum.source.y",
"targetX": "datum.target.x",
"targetY": "datum.target.y"
}
]
}这段代码增加了 stroke 和 strokeWidth 的条件判断。如果 active 信号有值（即鼠标悬停在节点上），并且链接的 source.name 或 target.name 等于 active 信号的值，则将链接的颜色设置为红色 ("red")，宽度设置为 2。否则，使用默认的颜色 #ccc 和宽度 0.5。 注意：请根据你的数据结构调整 datum.source.name 和 datum.target.name 的访问方式。
将以上代码片段添加到你的 Vega 配置中，即可实现节点悬停高亮链接的效果。完整的 Vega 配置如下（包含上述修改）：
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"description": "A node-link diagram with force-directed layout, depicting character co-occurrence in the novel Les Misérables.",
"width": 700,
"height": 500,
"padding": 0,
"autosize": "none",
"signals": [
{"name": "cx", "update": "width / 2"},
{"name": "cy", "update": "height / 2"},
{
"name": "nodeRadius",
"value": 8,
"bind": {"input": "range", "min": 1, "max": 50, "step": 1}
},
{
"name": "nodeCharge",
"value": -30,
"bind": {"input": "range", "min": -100, "max": 10, "step": 1}
},
{
"name": "linkDistance",
"value": 30,
"bind": {"input": "range", "min": 5, "max": 100, "step": 1}
},
{"name": "static", "value": true, "bind": {"input": "checkbox"}},
{
"description": "State variable for active node fix status.",
"name": "fix",
"value": false,
"on": [
{
"events": "symbol:mouseout[!event.buttons], window:mouseup",
"update": "false"
},
{"events": "symbol:mouseover", "update": "fix || true"},
{
"events": "[symbol:mousedown, window:mouseup] > window:mousemove!",
"update": "xy()",
"force": true
}
]
},
{
"description": "Graph node most recently interacted with.",
"name": "node",
"value": null,
"on": [
{"events": "symbol:mouseover", "update": "fix === true ? item() : node"}
]
},
{
"description": "Flag to restart Force simulation upon data changes.",
"name": "restart",
"value": false,
"on": [{"events": {"signal": "fix"}, "update": "fix && fix.length"}]
},
{
"name": "active",
"value": null,
"on": [
{"events": "symbol:mouseover", "update": "datum.name"},
{"events": "mouseover[!event.item]", "update": "null"}
]
}
],
"data": [
{
"name": "node-data",
"url": "data/miserables.json",
"format": {"type": "json", "property": "nodes"}
},
{
"name": "link-data",
"url": "data/miserables.json",
"format": {"type": "json", "property": "links"}
}
],
"scales": [
{
"name": "color",
"type": "ordinal",
"domain": {"data": "node-data", "field": "group"},
"range": {"scheme": "category20c"}
}
],
"marks": [
{
"name": "nodes",
"type": "symbol",
"zindex": 1,
"from": {"data": "node-data"},
"on": [
{
"trigger": "fix",
"modify": "node",
"values": "fix === true ? {fx: node.x, fy: node.y} : {fx: fix[0], fy: fix[1]}"
},
{"trigger": "!fix", "modify": "node", "values": "{fx: null, fy: null}"}
],
"encode": {
"enter": {"stroke": {"value": "white"}},
"update": {
"fill": {
"signal": "datum.name==active?'yellow': scale('color', datum.group)"
},
"size": {"signal": "2 * nodeRadius * nodeRadius"},
"cursor": {"value": "pointer"}
}
},
"transform": [
{
"type": "force",
"iterations": 300,
"restart": {"signal": "restart"},
"static": {"signal": "static"},
"signal": "force",
"forces": [
{"force": "center", "x": {"signal": "cx"}, "y": {"signal": "cy"}},
{"force": "collide", "radius": {"signal": "nodeRadius"}},
{"force": "nbody", "strength": {"signal": "nodeCharge"}},
{
"force": "link",
"links": "link-data",
"distance": {"signal": "linkDistance"}
}
]
}
]
},
{
"type": "path",
"from": {"data": "link-data"},
"interactive": false,
"encode": {
"update": {
"stroke": [
{
"test": "active && (datum.source.name === active || datum.target.name === active)",
"value": "red"
},
{"value": "#ccc"}
],
"strokeWidth": [
{
"test": "active && (datum.source.name === active || datum.target.name === active)",
"value": 2
},
{"value": 0.5}
]
}
},
"transform": [
{
"type": "linkpath",
"require": {"signal": "force"},
"shape": "line",
"sourceX": "datum.source.x",
"sourceY": "datum.source.y",
"targetX": "datum.target.x",
"targetY": "datum.target.y"
}
]
}
]
}通过定义交互信号和修改节点及链接的样式，我们成功实现了 Vega 力导向图中节点悬停高亮链接的功能。这可以帮助用户更好地理解和探索图数据，提高可视化的交互性和可读性。记住根据你的数据结构和需求调整代码，并注意潜在的性能问题。
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