# DataDiff (/docs/charts/data-diff)

DataDiff compares two versions of a dataset and gives each key a diverging bar: **removed leftward, added rightward,
both always drawn** on one symmetric shared scale. Net is a mark you can turn on, never a replacement for the two bars.
A table that added 500 rows and dropped 480 nets to +20, the same as one that added 20 and dropped nothing, and those
are not the same event.

```tsx
<DataDiff
  data={[
    { key: "users", added: 340, removed: 120 },
    { key: "orders", added: 88, removed: 30 },
    { key: "items", added: 40, removed: 20 },
    { key: "tags", added: 24, removed: 8 },
    { key: "notes", added: 12, removed: 6 },
    { key: "flags", added: 8, removed: 3 },
  ]}
  labels
  title="Schema diff"
  width={200}
  height={72}
/>
```

## Install

```tsx
import { DataDiff } from "@microcharts/react/data-diff";

<DataDiff data={diff} title="Schema diff" />
```

Setup (package + stylesheet): [Quickstart](/docs/quickstart#set-up-with-an-ai-agent) or paste [`/agent-setup.md`](/agent-setup.md) into your agent.

## Try it

```tsx
import { DataDiff } from "@microcharts/react/data-diff/interactive";

<DataDiff
  data={diff}
/>
```

## When to use it

Use it for a table cell per dataset version, a KPI card for a sync or import job, or any per-key added/removed audit
where churn matters. For a plain ranking reach for MiniBar; for parts of a single whole, SegmentedBar.

## Sizing

**key tags for standalone use**

```tsx
<DataDiff data={diff} labels />
```

**net tick + totals footer**

```tsx
<DataDiff data={diff} net label="totals" />
```

## Variants

`labels` prints in-chart key tags, `net` adds a per-row tick at added − removed, and `label="totals"` prints a
`+added / −removed` footer. One symmetric scale spans every row, so a big change never shrinks to fit a small one; to
compare across charts, pass them a shared `domain`.

```tsx
<DataDiff
  data={[
    { key: "users", added: 340, removed: 120 },
    { key: "orders", added: 88, removed: 30 },
    { key: "items", added: 40, removed: 20 },
  ]}
  labels
/>
<DataDiff
  data={[
    { key: "users", added: 340, removed: 120 },
    { key: "orders", added: 88, removed: 30 },
    { key: "items", added: 40, removed: 20 },
  ]}
  net
  label="totals"
/>
```

## Edge cases

```tsx
<DataDiff data={[]} />
```

```tsx
<DataDiff data={[{ key: "a", added: 0, removed: 0 }, { key: "b", added: 0, removed: 0 }]} />
```

An empty `data` array renders an empty chart and reports **"No data."** A non-empty diff where every key is 0/0 still
draws a hairline placeholder tick per row and reports **"No changes across 2 keys."** A key with no change keeps its
row, so the absence of a change never reads as the absence of the key.

## Four homes

**In a sentence**

```tsx
<p>
  Schema migration diff{" "}
  <span className="mc-inline">
    <DataDiff data={diff} summary={false} />
  </span>{" "}
  — 3 tables added, 1 column removed.
</p>
```

**In a table cell**

```tsx
<td>
  <DataDiff data={diff} />
</td>
```

**In a KPI card**

```tsx
<div className="kpi">
  <span className="figure">+3</span>
  <span className="unit">tables added</span>
  <DataDiff data={diff} />
</div>
```

**In a tab header**

```tsx
<button className="tab">
  users <DataDiff data={diff} />
</button>
```

## Accessibility

The accessible name states the totals, the key count, and the single largest change: **"+468 added, −170 removed across
3 keys; largest change: users (+220)."** The interactive entry steps the rows and announces each key's added, removed,
and net change.

The interactive entry follows the shared [interaction contract](/docs/accessibility#one-interaction-contract):
arrow keys rove between units on both axes, `Home` and `End` jump to the ends, and a click, tap, `Enter` or
`Space` selects a unit — pinning its readout so it survives blur, until you select it again, press `Escape`, or
press outside the chart. On touch, a tap pins and a drag scrubs.

## Props

| Prop | Type | Description |
| --- | --- | --- |
| `data` (required) | `{ key; added; removed }[]` | Per-key change counts — added and removed are non-negative magnitudes. |
| `labels` | `boolean` | In-chart key tags for standalone use (host tables carry keys by default). |
| `net` | `boolean` | A tick at added−removed per row — a summary mark, never the two bars. |
| `order` | `"data" \| "net" \| "magnitude"` | Default 'data' keeps input order (schema order is often meaningful). |
| `label` | `"totals" \| "none"` | 'totals' prints a +added / −removed footer. |
| `maxItems` | `number` | Row cap (default 12); rows beyond it are dropped with a dev warning. |
| `animate` | `boolean` | (interactive) Opt-in entrance motion when the chart mounts client-side — add `import "@microcharts/react/motion"` once. Inert on the server, on hydrated server HTML, and under `prefers-reduced-motion`. |

Plus the shared grammar — `data`, `domain`, `color`, `title`, `summary`, `format` — and the layout props (`width`, `height`, `className`, `style`) that every chart accepts. Interactive entries also share `animate` and `live`, and — wherever a chart has more than one navigable unit — `onActive`, `onSelect`, `selectedIndex` and `defaultSelectedIndex`; and — wherever the chart shows a hover value — `readout`. See [the shared grammar](/docs/quickstart#the-shared-grammar).