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use crate::{error::Error, prelude::Relation};
impl Relation {
/// Returns tuples that exist in `self` but not in `other` (`−`).
///
/// `a`
///
/// | `value` |
/// | --- |
/// | `1` |
/// | `2` |
/// | `3` |
///
/// `b`
///
/// | `value` |
/// | --- |
/// | `2` |
///
/// Output
///
/// | `value` |
/// | --- |
/// | `1` |
/// | `3` |
///
/// # Errors
///
/// Returns [`Error::HeadingMismatch`] if the relations do not have the same
/// heading.
///
/// # Example
///
/// ```rust
/// use darwen::prelude::{AttributeName, Heading, Relation, Scalar, ScalarType, Tuple};
///
/// let a = Relation::new_from_iter(
/// Heading::try_from(vec![(AttributeName::from("value"), ScalarType::Integer)])?,
/// vec![
/// Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(1))])?,
/// Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(2))])?,
/// Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(3))])?,
/// ],
/// )?;
/// let b = Relation::new_from_iter(
/// Heading::try_from(vec![(AttributeName::from("value"), ScalarType::Integer)])?,
/// vec![Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(2))])?],
/// )?;
///
/// let difference = a.difference(&b)?;
///
/// assert_eq!(
/// difference,
/// Relation::new_from_iter(
/// Heading::try_from(vec![(AttributeName::from("value"), ScalarType::Integer)])?,
/// vec![
/// Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(1))])?,
/// Tuple::try_from(vec![(AttributeName::from("value"), Scalar::Integer(3))])?,
/// ],
/// )?
/// );
/// # Ok::<(), darwen::prelude::Error>(())
/// ```
pub fn difference(&self, other: &Relation) -> Result<Relation, Error> {
if self.heading != other.heading {
return Err(Error::HeadingMismatch);
}
let mut relation = Relation::new(self.heading.clone());
for tuple in &self.body {
if other.body.contains(tuple) {
continue;
}
relation.insert(tuple.clone())?;
}
Ok(relation)
}
}
#[cfg(test)]
mod tests {
use crate::{
prelude::{Heading, Scalar, ScalarType, Tuple},
types::AttributeName,
};
use super::*;
#[test]
fn test_difference() {
let relation = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(2))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(3))]).unwrap(),
],
)
.unwrap();
let other = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(2))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(3))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(4))]).unwrap(),
],
)
.unwrap();
assert_eq!(
relation.difference(&other).unwrap(),
Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))])
.unwrap()
],
)
.unwrap()
);
assert_eq!(
other.difference(&relation).unwrap(),
Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(4))])
.unwrap()
],
)
.unwrap()
);
}
#[test]
fn test_difference_rejects_incompatible_headings() -> Result<(), Error> {
let lhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap()],
)?;
let rhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("bar"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("bar"), Scalar::Integer(1))]).unwrap()],
)?;
assert_eq!(lhs.difference(&rhs), Err(Error::HeadingMismatch));
Ok(())
}
#[test]
fn test_difference_with_self_is_empty() -> Result<(), Error> {
let relation = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(2))]).unwrap(),
],
)?;
assert_eq!(
relation.difference(&relation)?,
Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
Vec::new(),
)?
);
Ok(())
}
}