Struct arrow_schema::Schema

pub struct Schema {
    pub fields: Fields,
    pub metadata: HashMap<String, String>,
}

Describes the meta-data of an ordered sequence of relative types.

Note that this information is only part of the meta-data and not part of the physical memory layout.

Fields

fields: Fields

metadata: HashMap<String, String>

A map of key-value pairs containing additional meta data.

Implementations

impl Schema

pub fn empty() -> Self

Creates an empty Schema

pub fn new(fields: impl Into<Fields>) -> Self

Creates a new Schema from a sequence of Field values.

Example

let field_a = Field::new("a", DataType::Int64, false);
let field_b = Field::new("b", DataType::Boolean, false);

let schema = Schema::new(vec![field_a, field_b]);

pub fn new_with_metadata( fields: impl Into<Fields>, metadata: HashMap<String, String>, ) -> Self

Creates a new Schema from a sequence of Field values and adds additional metadata in form of key value pairs.

Example

let field_a = Field::new("a", DataType::Int64, false);
let field_b = Field::new("b", DataType::Boolean, false);

let mut metadata: HashMap<String, String> = HashMap::new();
metadata.insert("row_count".to_string(), "100".to_string());

let schema = Schema::new_with_metadata(vec![field_a, field_b], metadata);

pub fn with_metadata(self, metadata: HashMap<String, String>) -> Self

Sets the metadata of this Schema to be metadata and returns self

pub fn project(&self, indices: &[usize]) -> Result<Schema, ArrowError>

Returns a new schema with only the specified columns in the new schema This carries metadata from the parent schema over as well

pub fn try_merge( schemas: impl IntoIterator<Item = Self>, ) -> Result<Self, ArrowError>

Merge schema into self if it is compatible. Struct fields will be merged recursively.

Example:

let merged = Schema::try_merge(vec![
    Schema::new(vec![
        Field::new("c1", DataType::Int64, false),
        Field::new("c2", DataType::Utf8, false),
    ]),
    Schema::new(vec![
        Field::new("c1", DataType::Int64, true),
        Field::new("c2", DataType::Utf8, false),
        Field::new("c3", DataType::Utf8, false),
    ]),
]).unwrap();

assert_eq!(
    merged,
    Schema::new(vec![
        Field::new("c1", DataType::Int64, true),
        Field::new("c2", DataType::Utf8, false),
        Field::new("c3", DataType::Utf8, false),
    ]),
);

pub const fn fields(&self) -> &Fields

Returns an immutable reference of the vector of Field instances.

pub fn all_fields(&self) -> Vec<&Field>

Returns a vector with references to all fields (including nested fields)

pub fn field(&self, i: usize) -> &Field

Returns an immutable reference of a specific Field instance selected using an offset within the internal fields vector.

pub fn field_with_name(&self, name: &str) -> Result<&Field, ArrowError>

Returns an immutable reference of a specific Field instance selected by name.

pub fn fields_with_dict_id(&self, dict_id: i64) -> Vec<&Field>

Returns a vector of immutable references to all Field instances selected by the dictionary ID they use.

pub fn index_of(&self, name: &str) -> Result<usize, ArrowError>

Find the index of the column with the given name.

pub const fn metadata(&self) -> &HashMap<String, String>

Returns an immutable reference to the Map of custom metadata key-value pairs.

pub fn column_with_name(&self, name: &str) -> Option<(usize, &Field)>

Look up a column by name and return a immutable reference to the column along with its index.

pub fn contains(&self, other: &Schema) -> bool

Check to see if self is a superset of other schema.

In particular returns true if self.metadata is a superset of other.metadata and Fields::contains for self.fields and other.fields

In other words, any record that conforms to other should also conform to self.

Trait Implementations

impl Clone for Schema

fn clone(&self) -> Schema

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Schema

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Schema

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<&Schema> for SchemaBuilder

fn from(value: &Schema) -> Self

Converts to this type from the input type.

impl From<Schema> for SchemaBuilder

fn from(value: Schema) -> Self

Converts to this type from the input type.

impl Hash for Schema

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Schema

fn eq(&self, other: &Schema) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for Schema

impl StructuralPartialEq for Schema