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handle6 methods

Schema

Returned by DataHandle:schema(): the data's columns, by name or by position, and its metadata. Looking a column up by name takes the same time however many columns there are.

Obtained from
DataHandle:schema

The examples on this page start from:

lua
local sales = datumhue.bytes("day,loaves\nMon,12\nTue,\n"):csv()
local schema = sales:schema()

Methods 6

Schema:len

method
Schema:len() -> integer

Column count.

Schema:field

method
Schema:field(name: string) -> Field?

Look up a field by column name.

Example
-- nil for a column the table does not have.
local loaves = schema:field("loaves")
print(loaves:dtype(), loaves:is_nullable()) --> int64 true
print(schema:field("price")) --> nil

Schema:field_at

method
Schema:field_at(i: integer) -> Field?

Look up a field by 1-based position.

Example
-- Positions count from 1, in column order.
print(schema:field_at(1).name, schema:field_at(3)) --> day nil

Schema:fields

method
Schema:fields() -> function, any, nil

Iterator: for i, f in s:fields() do yields (integer, Field) pairs.

Example
for i, field in schema:fields() do
    print(i, field.name, field:dtype())
end

Schema:metadata

method
Schema:metadata() -> table

Schema-level metadata as a string->string table.

Schema:meta

method
Schema:meta(key: string) -> string?

A single schema-level metadata entry.

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