QGIS/resources/function_help/json/count

{
  "name": "count",
  "type": "function",
  "groups": ["Aggregates"],
  "description": "Returns the count of matching features.",
  "arguments": [{
    "arg": "expression",
    "description": "sub expression of field to aggregate"
  }, {
    "arg": "group_by",
    "optional": true,
    "description": "optional expression to use to group aggregate calculations"
  }, {
    "arg": "filter",
    "optional": true,
    "description": "optional expression to use to filter features used to calculate aggregate"
  }],
  "examples": [{
    "expression": "count(\"stations\",group_by:=\"state\")",
    "returns": "count of stations, grouped by state field"
  }],
  "tags": ["aggregate", "features", "matching", "count"]
}