Struct parquet::arrow::ProjectionMask

pub struct ProjectionMask { /* private fields */ }

A ProjectionMask identifies a set of columns within a potentially nested schema to project

In particular, a ProjectionMask can be constructed from a list of leaf column indices or root column indices where:

• Root columns are the direct children of the root schema, enumerated in order
• Leaf columns are the child-less leaves of the schema as enumerated by a depth-first search

For example, the schema

message schema {
  REQUIRED boolean         leaf_1;
  REQUIRED GROUP group {
    OPTIONAL int32 leaf_2;
    OPTIONAL int64 leaf_3;
  }
}

Has roots ["leaf_1", "group"] and leaves ["leaf_1", "leaf_2", "leaf_3"]

For non-nested schemas, i.e. those containing only primitive columns, the root and leaves are the same

Implementations

impl ProjectionMask

pub fn all() -> Self

Create a ProjectionMask which selects all columns

pub fn leaves( schema: &SchemaDescriptor, indices: impl IntoIterator<Item = usize>, ) -> Self

Create a ProjectionMask which selects only the specified leaf columns

Note: repeated or out of order indices will not impact the final mask

i.e. [0, 1, 2] will construct the same mask as [1, 0, 0, 2]

pub fn roots( schema: &SchemaDescriptor, indices: impl IntoIterator<Item = usize>, ) -> Self

Create a ProjectionMask which selects only the specified root columns

Note: repeated or out of order indices will not impact the final mask

i.e. [0, 1, 2] will construct the same mask as [1, 0, 0, 2]

pub fn leaf_included(&self, leaf_idx: usize) -> bool

Returns true if the leaf column leaf_idx is included by the mask

Trait Implementations

impl Clone for ProjectionMask

fn clone(&self) -> ProjectionMask

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for ProjectionMask

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

Formats the value using the given formatter.