improve docs

Author: thomasp85

doc/syntax/clause/draw.qmd

@@ -86,7 +86,8 @@ The `aggregate` setting takes a single string or an array of strings. Each strin
 
 A numeric mapping is dropped from the layer with a warning, when it has neither a target nor an applicable default.
 
-The simple functions are:
+##### Aggregate functions
+Aggregation can either be a simple function or a band function. The simple functions are:
 
 * `'count'`: Non-null tally of the bound column.
 * `'sum'` and `'prod'`: The sum or product
@@ -105,7 +106,8 @@ Allowed offsets are: `'mean'`, `'median'`, `'geomean'`, `'harmean'`, `'rms'`, `'
 
 Allowed expansions are: `'sdev'`, `'se'`, `'var'`, `'iqr'`, and `'range'`
 
-You can also target the same aesthetic more than once to produce **multiple rows per group** — one for each function. For example `aggregate => ('y:min', 'y:max')` emits a min row and a max row per group, so a single `DRAW line` produces two summary lines that connect within each group rather than across them. When multiple rows are created, a synthetic `aggregate` column is made that tags each row with the name of the aggregation function. You can use this with a `REMAPPING` to drive another aesthetic — e.g. `REMAPPING aggregate AS stroke` to colour the two lines differently. The column's value is built from the per-row function names of the *exploded* targets, deduplicated, and joined with `/`:
+##### Exploded aggregation
+You can also target the same aesthetic more than once to produce *multiple rows per group* — one for each function. We call that *exploded aggregation*. For example `aggregate => ('y:min', 'y:max')` emits a min row and a max row per group, so a single `DRAW line` produces two summary lines that connect within each group rather than across them. When multiple rows are created, a synthetic `aggregate` column is made that tags each row with the name of the aggregation function. You can use this with a `REMAPPING` to drive another aesthetic — e.g. `REMAPPING aggregate AS stroke` to colour the two lines differently. The column's value is built from the per-row function names of the *exploded* targets, deduplicated, and joined with `/`:
 
 * `aggregate => ('y:min', 'y:max')` → rows tagged `'min'`, `'max'`.
 * `aggregate => ('y:min', 'y:max', 'color:median')` → rows tagged `'min'`, `'max'` (the single-function `color` target is recycled across rows and is not part of the label).

doc/syntax/layer/type/tile.qmd

@@ -99,10 +99,10 @@ DRAW tile
 Building a heatmap from raw rows by aggregating per cell.
 
 ```{ggsql}
-VISUALISE FROM ggsql:airquality
+VISUALISE FROM ggsql:penguins
 DRAW tile
-  MAPPING Month AS x, Day AS y, Temp AS fill
-  SETTING aggregate => 'mean'
+  MAPPING species AS x, sex AS y, body_mass AS fill
+  SETTING aggregate => 'mean', opacity => 1
 ```
 
 Using a tile as an annotation. Note we're using the `PLACE` clause here instead of `DRAW` because we're not mapping from data.

src/plot/layer/geom/mod.rs

@@ -305,7 +305,10 @@ pub trait GeomTrait: std::fmt::Debug + std::fmt::Display + Send + Sync {
 
 /// True when `parameters["aggregate"]` is set to a non-null string or array.
 pub(crate) fn has_aggregate_param(parameters: &HashMap<String, ParameterValue>) -> bool {
-    matches!(parameters.get("aggregate"), Some(ParameterValue::String(_)) | Some(ParameterValue::Array(_)))
+    matches!(
+        parameters.get("aggregate"),
+        Some(ParameterValue::String(_)) | Some(ParameterValue::Array(_))
+    )
 }
 
 /// Wrapper struct for geom trait objects