Statistics

The Statistics operator is a plot operator that computes count statistics over

• a selection of numerical columns of a single vector dataset, or
• a selection of bands of a single raster dataset.

The output is a Vega-Lite table with one row per attribute or band. The raw statistics of each row are in the data.values of the Vega-Lite spec in vegaSpec, with the attribute or band in name.

For instance, you want to get an overview of a raster data source. Then, you can use this operator to get basic count statistics.

Vector Data

In the case of vector data, the operator generates one statistic for each of the selected numerical attributes. The operator returns an error if one of the selected attributes is not numeric.

Raster Data

For raster data, the operator generates one statistic for each of the selected bands. It only considers the pixels that intersect the query rectangle.

Errors

The operator returns an error in the following cases.

• Vector data: One of the selected attributes is not numeric.
• Vector data: One of the selected attributes does not exist.
• Raster data: One of the selected attributes (bands) does not exist.

Example Output

The data.values of the Vega-Lite spec:

[
    {
        "name": "ndvi",
        "valueCount": 6,
        "validCount": 6,
        "min": 1.0,
        "max": 6.0,
        "mean": 3.5,
        "stddev": 1.707,
        "percentiles": [
            {
                "percentile": 0.25,
                "value": 2.0
            },
            {
                "percentile": 0.5,
                "value": 3.5
            },
            {
                "percentile": 0.75,
                "value": 5.0
            }
        ]
    }
]

Parameters

Name	Type	Description	Examples
attributes	AttributeSelection	Optional: The attributes to generate statistics for. For vector data, these are numeric columns, for raster data, these are bands. Defaults to all, i.e., all numeric columns or all bands.	{"type":"names","values":["ndvi"]}
percentiles	array	The percentiles to compute for each attribute.	[0.25,0.5,0.75]

Sources

Name	Type	Description
source	SingleRasterOrVectorOperator	It is either a single RasterOperator or a single VectorOperator

Examples

{
    "type": "Statistics",
    "params": {
        "attributes": {
            "type": "names",
            "values": ["ndvi"]
        },
        "percentiles": [0.25, 0.5, 0.75]
    },
    "sources": {
        "source": {
            "type": "GdalSource",
            "params": {
                "data": "ndvi"
            }
        }
    }
}