This is an example dataset that demonstrates how to build visualizations using the "Vega Graph Spec". We are using Yields of Barley Based on the Trellis Display - one of the examples from vega editor - and displaying it here, on DataHub with small modifications in vega-spec.
We assume that you are familiar with what datapackage.json is and its specifications.
To create graphs for your tabular data, the datapackage.json should include the views attribute that is used for visualizations.
If you are familiar with Vega specifications, you probably would like to use all its features. To use it, inside views you should set specType to "vega" and define some graph specifications in spec property. See below for more details.
This is the views property that is used for this page:
{
...,
"views": [
{
"title": "DEMO Vega spec view",
"resources": ["barley"],
"specType": "vega",
"spec": {
"$schema": "https://vega.github.io/schema/vega/v3.0.json",
"width": 200,
"padding": 5,
"signals": [
{
"name": "offset",
"value": 15
},
{
"name": "cellHeight",
"value": 100
},
{
"name": "height",
"update": "6 * (offset + cellHeight)"
}
],
"data": [
{
"name": "barley"
}
],
"scales": [
{
"name": "gscale",
"type": "band",
"range": [
0,
{
"signal": "height"
}
],
"round": true,
"domain": {
"data": "barley",
"field": "site",
"sort": {
"field": "yield",
"op": "median",
"order": "descending"
}
}
},
{
"name": "xscale",
"type": "linear",
"nice": true,
"range": "width",
"round": true,
"domain": {
"data": "barley",
"field": "yield"
}
},
{
"name": "cscale",
"type": "ordinal",
"range": "category",
"domain": {
"data": "barley",
"field": "year"
}
}
],
"axes": [
{
"orient": "bottom",
"scale": "xscale",
"zindex": 1
}
],
"legends": [
{
"stroke": "cscale",
"title": "Year",
"padding": 4,
"encode": {
"symbols": {
"enter": {
"strokeWidth": {
"value": 2
},
"size": {
"value": 50
}
}
}
}
}
],
"marks": [
{
"name": "site",
"type": "group",
"from": {
"facet": {
"data": "barley",
"name": "sites",
"groupby": "site"
}
},
"encode": {
"enter": {
"y": {
"scale": "gscale",
"field": "site",
"offset": {
"signal": "offset"
}
},
"height": {
"signal": "cellHeight"
},
"width": {
"signal": "width"
},
"stroke": {
"value": "#ccc"
}
}
},
"scales": [
{
"name": "yscale",
"type": "point",
"range": [
0,
{
"signal": "cellHeight"
}
],
"padding": 1,
"round": true,
"domain": {
"data": "barley",
"field": "variety",
"sort": {
"field": "yield",
"op": "median",
"order": "descending"
}
}
}
],
"axes": [
{
"orient": "left",
"scale": "yscale",
"tickSize": 0,
"domain": false,
"grid": true,
"encode": {
"grid": {
"enter": {
"strokeDash": {
"value": [
3,
3
]
}
}
}
}
},
{
"orient": "right",
"scale": "yscale",
"tickSize": 0,
"domain": false
}
],
"marks": [
{
"type": "symbol",
"from": {
"data": "sites"
},
"encode": {
"enter": {
"x": {
"scale": "xscale",
"field": "yield"
},
"y": {
"scale": "yscale",
"field": "variety"
},
"stroke": {
"scale": "cscale",
"field": "year"
},
"strokeWidth": {
"value": 2
},
"size": {
"value": 50
}
}
}
}
]
},
{
"type": "text",
"from": {
"data": "site"
},
"encode": {
"enter": {
"x": {
"field": "width",
"mult": 0.5
},
"y": {
"field": "y"
},
"fontSize": {
"value": 11
},
"fontWeight": {
"value": "bold"
},
"text": {
"field": "datum.site"
},
"align": {
"value": "center"
},
"baseline": {
"value": "bottom"
},
"fill": {
"value": "#000"
}
}
}
}
]
}
}
]
}
You can use almost the same specifications inside spec attribute, that are used for setting the Vega graphs. Only difference is that in data property, url and path attributes are moved out. Instead we use name attribute to reference to a resource. Note, how we created a new object inside data property - {"name": "flights-airport"} to reference it to a resource (this names are identical to names of resources):
...
"spec": {
...
"data": [
{
"name": "barley"
}
...
]
...
}
Outside of spec attribute there are some other important parameters to note:
| Attribute | Type | Description |
|---|---|---|
| name | String | Unique identifier for view within list of views. |
| title | String | Title for the graph. |
| resources | Array | Data sources for this spec. It can be either resource name or index. By default it is the first resource. |
| specType | String | Available options: simple, vega, plotly (Required). |