# Project

Keeps only a subset of attributes.

## Signature

project(operand: Relation, attributes: AttrList) -> Relation

## Examples

project(suppliers, [:city])

project(suppliers, [:city], allbut: true)

## Description

Computes the relation obtained by projecting tuples from `operand` on a
subset of their attributes.

This operator supports an ALL BUT variant, through the `allbut` option.
When set to true, the operator _removes_ specified attributes instead of
keeping them. An `allbut` operator is also provided that has the same
effect.

## Implementation notes

Unlike SQL, this operator ALWAYS remove duplicates. There is no way, in
Alf, to compute _bags_ of tuples.