# `Macaw.Data.Operations.Aggregates`
[🔗](https://github.com/dcoai/macaw_data/blob/v0.5.3/lib/macaw/data/operations/aggregates.ex#L1)

The statistics of `macaw_data`'s package (spec/04 §5), each an aggregate
(`Macaw.Data.Aggregate`) ported from visualize's `Visualize.Data`:

| Name | Value | Of no readings | Output type | Unit |
|---|---|---|---|---|
| `count` | the number of readings | `0` | `:number` | dropped |
| `distinct` | the number of distinct readings (`===`, a category by spelling) | `0` | `:number` | dropped |
| `min`, `max` | the least, the greatest reading, numbers or times | `nil` | the input's | kept |
| `extent` | `[min, max]` | `nil` | `:term` | kept |
| `sum` | the sum of numbers | `0` | `:number` | kept |
| `mean` | the arithmetic mean | `nil` | `:number` | kept |
| `median` | the middle reading, or the mean of the two middles | `nil` | `:number` | kept |
| `quantile` | linear interpolation at `(n − 1) · p` | `nil` | `:number` | kept |
| `variance` | the sample variance | `nil`, and of one | `:number` | dropped |
| `deviation` | its square root | `nil`, and of one | `:number` | kept |
| `slope` | the least-squares slope; a number is the point `[i, v]` | `nil`, of one, or every `x` equal | `:number` | dropped |
| `delta` | the last reading minus the first | `nil` (`0` of one) | `:number` | kept |

The readings come with every `nil` dropped. A reading of the wrong kind raises
`ArgumentError` naming the aggregate and the reading. Every statistic but `median` and
`quantile` has the streaming form, and its `reduce/2` **is** that form folded over the
readings, so the two are equal by construction: the mean is a running sum over a count,
the variance and the slope Welford's one-pass updates, which agree with visualize's
two-pass values to within floating-point rounding.

# `all`

```elixir
@spec all() :: [module()]
```

The modules of the thirteen statistics, in spec/04 §5's order.

---

*Consult [api-reference.md](api-reference.md) for complete listing*