Histogram

A histogram answers “how is this number distributed?” Plot expresses it as a rectY mark wrapped in a binX transform: the transform groups rows into bins, the mark draws a bar for each bin’s count.

Basic

```plot view=order_amounts
Plot.rectY(data, Plot.binX({ y: "count" }, { x: "amount" }))
```

With a target line

```plot view=order_amounts
{
  marks: [
    Plot.rectY(data, Plot.binX({ y: "count" }, { x: "amount" })),
    Plot.ruleX([100], { stroke: "tomato", strokeDasharray: "4 2" }),
  ]
}
```

Stacked by group

Pass a fill channel; bins stack by group at each x.

```plot view=order_amounts_by_segment
Plot.rectY(data, Plot.binX({ y: "count" }, { x: "amount", fill: "segment" }))
```

Common options

Option	Meaning
x	column name (the numeric variable being binned)
thresholds	bin count, e.g. 24; or an array of cut points; or a function
fill	column name → grouping (rows in the same bin stack by this)
Plot.binX({ y: "count" }, ...)	count rows per bin (most common)
Plot.binX({ y: "sum" }, ...)	sum a column per bin (set y2: "amount")
Plot.binX({ y: "mean" }, ...)	mean a column per bin
interval	for date bins: "day", "month", "year", etc.
cumulative	true for a cumulative histogram

See Observable Plot — bin and rect.