---
id: hierarchy
title: Hierarchical grid functions
sidebar_label: Hierarchy
slug: /api/hierarchy
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

These functions permit moving between resolutions in the H3 grid system. The functions produce parent (coarser) or children (finer) cells.

## h3ToParent

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
H3Index h3ToParent(H3Index h, int parentRes);
```

</TabItem>
<TabItem value="python">

```py
h3.h3_to_parent(h, parent_res)
```

</TabItem>
<TabItem value="java">

```java
long h3ToParent(long h3, int parentRes);
String h3ToParent(String h3Address, int parentRes);
```

</TabItem>
<TabItem value="javascript">

```js
h3.h3ToParent(h3Index, parentRes)
```

```js live
function example() {
  const h = '85283473fffffff';
  return h3.h3ToParent(h, 4);
}
```

</TabItem>
</Tabs>

Returns the parent (coarser) index containing `h`.

## h3ToChildren

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
void h3ToChildren(H3Index h, int childRes, H3Index *children);
```

</TabItem>
<TabItem value="python">

```py
h3.h3_to_children(h, child_res)
```

</TabItem>
<TabItem value="java">

```java
List<Long> h3ToChildren(long h3, int childRes);
List<String> h3ToChildren(String h3Address, int childRes);
```

</TabItem>
<TabItem value="javascript">

```js
h3.h3ToChildren(h3Index, childRes)
```

```js live
function example() {
  const h = '85283473fffffff';
  return h3.h3ToChildren(h, 6);
}
```

</TabItem>
</Tabs>

Populates `children` with the indexes contained by `h` at resolution `childRes`. `children` must be an array of at least size `maxH3ToChildrenSize(h, childRes)`.

## maxH3ToChildrenSize

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
int maxH3ToChildrenSize(H3Index h, int childRes);
```

</TabItem>
<TabItem value="python">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
<TabItem value="java">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
<TabItem value="javascript">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
</Tabs>

Returns the parent (coarser) index containing `h`.

## h3ToCenterChild

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
H3Index h3ToCenterChild(H3Index h, int childRes);
```

</TabItem>
<TabItem value="python">

```py
h3.h3_to_center_child(h3, child_res)
```

</TabItem>
<TabItem value="java">

```java
long h3ToCenterChild(long h3, int childRes);
String h3ToCenterChild(String h3, int childRes);
```

</TabItem>
<TabItem value="javascript">

```js
h3.h3ToCenterChild(h, childRes)
```

```js live
function example() {
  const h = '85283473fffffff';
  return h3.h3ToCenterChild(h, 7);
}
```

</TabItem>
</Tabs>

Returns the center child (finer) index contained by `h` at resolution `childRes`.

## compact

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
int compact(const H3Index *h3Set, H3Index *compactedSet, const int numHexes);
```

</TabItem>
<TabItem value="python">

```py
h3.compact(hexes)
```

</TabItem>
<TabItem value="java">

```java
List<Long> compact(Collection<Long> h3);
List<String> compactAddress(Collection<String> h3);
```

</TabItem>
<TabItem value="javascript">

```js
h3.compact(hexes)
```

```js live
function example() {
  const h = '85283473fffffff';
  const nearby = h3.kRing(h, 4);
  return h3.compact(nearby);
}
```

</TabItem>
</Tabs>

Compacts the set `h3Set` of indexes as best as possible, into the array `compactedSet`. `compactedSet` must be at least the size of `h3Set` in case the set cannot be compacted.

Returns 0 on success.

## uncompact

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
int uncompact(const H3Index *compactedSet, const int numHexes, H3Index *h3Set, const int maxHexes, const int res);
```

</TabItem>
<TabItem value="python">

```py
h3.uncompact(hexes, res)
```

</TabItem>
<TabItem value="java">

```java
List<Long> uncompact(Collection<Long> h3, int res);
List<String> uncompactAddress(Collection<String> h3, int res);
```

</TabItem>
<TabItem value="javascript">

```js
h3.uncompact(hexes, res)
```

```js live
function example() {
  const h = '85283473fffffff';
  const nearby = h3.kRing(h, 4);
  const compacted = h3.compact(nearby);
  return h3.uncompact(compacted, 5);
}
```

</TabItem>
</Tabs>

Uncompacts the set `compactedSet` of indexes to the resolution `res`. `h3Set` must be at least of size `maxUncompactSize(compactedSet, numHexes, res)`.

Returns 0 on success.

## maxUncompactSize

<Tabs
  groupId="language"
  defaultValue="c"
  values={[
    {label: 'C', value: 'c'},
    {label: 'Python', value: 'python'},
    {label: 'Java', value: 'java'},
    {label: 'JavaScript (Live)', value: 'javascript'},
  ]
}>
<TabItem value="c">

```c
int maxUncompactSize(const H3Index *compactedSet, const int numHexes, const int res)
```

</TabItem>
<TabItem value="python">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
<TabItem value="java">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
<TabItem value="javascript">

:::note

This function exists for memory management and is not exposed.

:::

</TabItem>
</Tabs>

Returns the size of the array needed by `uncompact`.
