如何使用 "datum" 在 Vega 中放置 x 轴标签？
How to put x-axis labels in Vega using "datum"?
在 Vega 中，我想在 x 轴标签中放置一个表达式，其中包含来自“参考”列的数据。我只能为所有值放置一个固定标签（第 67 行注释），但是当我尝试在文本中放置表达式“datum.reference”时，我做不到（第 68 行）。你可以帮帮我吗？非常感谢您
代码如下：
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28, "reference": "ref1"},
{"category": "B", "amount": 55, "reference": "ref2"},
{"category": "C", "amount": 43, "reference": "ref3"},
{"category": "D", "amount": 91, "reference": "ref1"},
{"category": "E", "amount": 81, "reference": "ref4"},
{"category": "F", "amount": 53, "reference": "ref5"},
{"category": "G", "amount": 19, "reference": "ref6"},
{"category": "H", "amount": 87, "reference": "ref7"}
]
}
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
//"text": {"value": "x_label"}, // Line 67: This is fine
"text": {"expr": "datum.reference"}, // Line 68: Here, I have the problem
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}
```
首先，Vega axis中的“datum”不引用数据集“table”中的任何项目。相反，Vega axis 使用内部生成的数据集，该数据集基于为该轴定义的 scale。
参见Vega documentation for "axis"。该文档还指出（没有给出示例）：
Custom text can be defined using the "text" property for labels. For example, one could define an ordinal scale that serves as a lookup table from axis values to axis label text.
这是一个示例，说明如何为此目的使用查找数据集和 scale。请注意，“category”的所有值必须是唯一的，“reference”的所有值必须是唯一的。
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28},
{"category": "B", "amount": 55},
{"category": "C", "amount": 43},
{"category": "D", "amount": 91},
{"category": "E", "amount": 81},
{"category": "F", "amount": 53},
{"category": "G", "amount": 19},
{"category": "H", "amount": 87}
]
},
{
"name": "data_lookup",
"values": [
{"category": "A", "reference": "ref1"},
{"category": "B", "reference": "ref2"},
{"category": "C", "reference": "ref3"},
{"category": "D", "reference": "ref10"},
{"category": "E", "reference": "ref4"},
{"category": "F", "reference": "ref5"},
{"category": "G", "reference": "ref6"},
{"category": "H", "reference": "ref7"}
]
}
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "scale_lookup",
"type": "ordinal",
"domain": {"data": "data_lookup", "field": "category"},
"range": {"data": "data_lookup", "field": "reference"}
},
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
"text": {"signal": "scale('scale_lookup', datum.value)"},
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}
我已经用非常简单的方法解决了这个问题。只需创建一个连接两个字段的转换，然后使用该新列来表示数据。无论如何，非常感谢您提供我觉得非常有趣和有用的其他解决方案。
这里我提供我想要实现的代码
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28, "reference": "ref1"},
{"category": "B", "amount": 55, "reference": "ref2"},
{"category": "C", "amount": 43, "reference": "ref3"},
{"category": "D", "amount": 91, "reference": "ref1"},
{"category": "E", "amount": 81, "reference": "ref4"},
{"category": "F", "amount": 53, "reference": "ref5"},
{"category": "G", "amount": 19, "reference": "ref6"},
{"category": "H", "amount": 87, "reference": "ref7"}
],
"transform":[
{"type": "formula",
"expr": "datum.category + ' (' + datum.reference + ')' ",
"as": "category(ref)"}
]
},
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category(ref)"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category(ref)"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}
在 Vega 中，我想在 x 轴标签中放置一个表达式，其中包含来自“参考”列的数据。我只能为所有值放置一个固定标签（第 67 行注释），但是当我尝试在文本中放置表达式“datum.reference”时，我做不到（第 68 行）。你可以帮帮我吗？非常感谢您
代码如下：
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28, "reference": "ref1"},
{"category": "B", "amount": 55, "reference": "ref2"},
{"category": "C", "amount": 43, "reference": "ref3"},
{"category": "D", "amount": 91, "reference": "ref1"},
{"category": "E", "amount": 81, "reference": "ref4"},
{"category": "F", "amount": 53, "reference": "ref5"},
{"category": "G", "amount": 19, "reference": "ref6"},
{"category": "H", "amount": 87, "reference": "ref7"}
]
}
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
//"text": {"value": "x_label"}, // Line 67: This is fine
"text": {"expr": "datum.reference"}, // Line 68: Here, I have the problem
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}
```
首先，Vega axis中的“datum”不引用数据集“table”中的任何项目。相反，Vega axis 使用内部生成的数据集，该数据集基于为该轴定义的 scale。
参见Vega documentation for "axis"。该文档还指出（没有给出示例）：
Custom text can be defined using the "text" property for labels. For example, one could define an ordinal scale that serves as a lookup table from axis values to axis label text.
这是一个示例，说明如何为此目的使用查找数据集和 scale。请注意，“category”的所有值必须是唯一的，“reference”的所有值必须是唯一的。
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28},
{"category": "B", "amount": 55},
{"category": "C", "amount": 43},
{"category": "D", "amount": 91},
{"category": "E", "amount": 81},
{"category": "F", "amount": 53},
{"category": "G", "amount": 19},
{"category": "H", "amount": 87}
]
},
{
"name": "data_lookup",
"values": [
{"category": "A", "reference": "ref1"},
{"category": "B", "reference": "ref2"},
{"category": "C", "reference": "ref3"},
{"category": "D", "reference": "ref10"},
{"category": "E", "reference": "ref4"},
{"category": "F", "reference": "ref5"},
{"category": "G", "reference": "ref6"},
{"category": "H", "reference": "ref7"}
]
}
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "scale_lookup",
"type": "ordinal",
"domain": {"data": "data_lookup", "field": "category"},
"range": {"data": "data_lookup", "field": "reference"}
},
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
"text": {"signal": "scale('scale_lookup', datum.value)"},
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}
我已经用非常简单的方法解决了这个问题。只需创建一个连接两个字段的转换，然后使用该新列来表示数据。无论如何，非常感谢您提供我觉得非常有趣和有用的其他解决方案。
这里我提供我想要实现的代码
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,
"autosize": "pad",
"data": [
{
"name": "table",
"values": [
{"category": "A", "amount": 28, "reference": "ref1"},
{"category": "B", "amount": 55, "reference": "ref2"},
{"category": "C", "amount": 43, "reference": "ref3"},
{"category": "D", "amount": 91, "reference": "ref1"},
{"category": "E", "amount": 81, "reference": "ref4"},
{"category": "F", "amount": 53, "reference": "ref5"},
{"category": "G", "amount": 19, "reference": "ref6"},
{"category": "H", "amount": 87, "reference": "ref7"}
],
"transform":[
{"type": "formula",
"expr": "datum.category + ' (' + datum.reference + ')' ",
"as": "category(ref)"}
]
},
],
"signals": [
{
"name": "tooltip",
"value": {},
"on": [
{"events": "rect:mouseover", "update": "datum"},
{"events": "rect:mouseout", "update": "{}"}
]
}
],
"scales": [
{
"name": "xscale",
"type": "band",
"domain": {"data": "table", "field": "category(ref)"},
"range": "width",
"padding": 0.05,
"round": true
},
{
"name": "yscale",
"domain": {"data": "table", "field": "amount"},
"nice": true,
"range": "height"
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"title": "X-Axis",
"encode": {
"ticks": {
"update": {
"stroke": {"value": "steelblue"}
}
},
"labels": {
"interactive": true,
"update": {
"fill": {"value": "steelblue"},
"angle": {"value": 50},
"fontSize": {"value": 14},
"align": {"value": "left"},
"baseline": {"value": "middle"},
"dx": {"value": 3}
},
"hover": {
"fill": {"value": "firebrick"}
}
},
"title": {
"update": {
"fontSize": {"value": 16}
}
},
"domain": {
"update": {
"stroke": {"value": "#333"},
"strokeWidth": {"value": 1.5}
}
}
}
},
{ "orient": "left",
"scale": "yscale",
"title": "Y-Axis",
"tickCount": 4,"offset": 6 }
],
"marks": [
{
"type": "rect",
"from": {"data":"table"},
"encode": {
"enter": {
"x": {"scale": "xscale", "field": "category(ref)"},
"width": {"scale": "xscale", "band": 1},
"y": {"scale": "yscale", "field": "amount"},
"y2": {"scale": "yscale", "value": 0}
},
"update": {
"fill": {"value": "steelblue"}
},
"hover": {
"fill": {"value": "red"}
}
}
},
{
"type": "text",
"encode": {
"enter": {
"align": {"value": "center"},
"baseline": {"value": "bottom"},
"fill": {"value": "#333"}
},
"update": {
"x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
"y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
"text": {"signal": "tooltip.amount"},
"fillOpacity": [
{"test": "isNaN(tooltip.amount)", "value": 0},
{"value": 1}
]
}
}
}
]
}