How to Transform Data with Pivot in Vega-Lite?

Have you ever needed to reshape your data into a matrix or cross-tabulation format? The pivot transform in Vega-Lite is your go-to tool! This transform converts unique values from a specified field into new aggregated fields (columns) in the output stream. Let's dive into the details and see some examples to understand how it works.

What Does Pivot Do?

The pivot transform in Vega-Lite helps you reshape your data by turning the unique values from one field into new columns, and aggregating the data into these new columns. You can also group by additional fields to organize your data into rows.

Pivot Transform Parameters

Here's a quick rundown of the parameters you can use with the pivot transform:

• pivot: The field containing the unique values you want to turn into new columns.
• value: The field whose values will populate the new columns.
• groupby: (Optional) Fields to group by, creating individual rows for each group.
• limit: (Optional) Limit the number of pivoted columns.
• op: (Optional) Aggregation operation to apply. Default is "sum".

Example: Olympic Medal Counts

Let’s consider an example with Olympic medal counts for various countries:

Input Data:

[
  {"country": "Norway", "type": "gold", "count": 14},
  {"country": "Norway", "type": "silver", "count": 14},
  {"country": "Norway", "type": "bronze", "count": 11},
  {"country": "Germany", "type": "gold", "count": 14},
  {"country": "Germany", "type": "silver", "count": 10},
  {"country": "Germany", "type": "bronze", "count": 7},
  {"country": "Canada", "type": "gold", "count": 11},
  {"country": "Canada", "type": "silver", "count": 8},
  {"country": "Canada", "type": "bronze", "count": 10}
]

Pivot Transform Configuration:

{
  "pivot": "type",
  "groupby": ["country"],
  "value": "count"
}

Output Data:

[
  {"country": "Norway", "gold": 14, "silver": 14, "bronze": 11},
  {"country": "Germany", "gold": 14, "silver": 10, "bronze": 7},
  {"country": "Canada", "gold": 11, "silver": 8, "bronze": 10}
]

As you can see, each country now has fields for gold, silver, and bronze, with the counts aggregated accordingly.

Interactive Examples

Explore these interactive examples to see the pivot transform in action:

• Bar Chart with Pivot: Bar Column Pivot (opens in a new tab)
• Interactive Multi-Line Chart with Tooltip: Interactive Multi-Line Pivot Tooltip (opens in a new tab)

FAQs

Q1: When should I use the pivot transform?

Use the pivot transform when you need to reshape your data into a cross-tabulation or matrix format, where unique values from one field become new columns.

Q2: Can I limit the number of pivoted columns?

Yes, you can use the limit parameter to control the number of columns resulting from the pivot transformation.

Q3: What aggregation operations can I use with pivot?

By default, the op parameter in the pivot transform uses "sum", but you can use other aggregation operations like "mean", "max", "min", etc.

Feel free to experiment with these transforms and examples to get a better grasp of how the pivot transform can make your data visualization more effective!

Remember, with vizGPT's chat interface, you can easily create sophisticated data visualizations using these transformations without needing to dive into complex code. Happy visualizing!