# `Arrow.Field`

A named column within a schema. Holds the logical type, nullability, an
optional per-field metadata map, the child fields used by nested types
(`List`, `Struct`), and an optional `Arrow.Type.DictionaryEncoding` when
the field is dictionary-encoded.

Dictionary encoding in Arrow is a *property of the field*, not a type:
the `type` continues to describe what the dictionary stores (e.g.
`Utf8`), while `dictionary.index_type` describes the integer type used
in record batches to reference dictionary entries.

# `metadata`

```elixir
@type metadata() :: %{optional(String.t()) => String.t()}
```

# `t`

```elixir
@type t() :: %Arrow.Field{
  children: [t()],
  dictionary: Arrow.Type.DictionaryEncoding.t() | nil,
  metadata: metadata(),
  name: String.t(),
  nullable: boolean(),
  type: Arrow.Type.t()
}
```

# `find_by_dictionary_id`

```elixir
@spec find_by_dictionary_id(Arrow.Schema.t() | [t()], non_neg_integer()) :: t() | nil
```

Walks the field tree under `schema_or_fields` and returns the first
field whose dictionary annotation has the given id, or `nil`.

# `value_field`

```elixir
@spec value_field(t()) :: t()
```

Returns the field with its `dictionary` annotation stripped — i.e. a
field that describes the *value* type only. Used when decoding the
contents of a `DictionaryBatch`, where the buffers carry the dictionary
values rather than indices.

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