Predicate
A predicate is a condition, expression, or function evaluated against an input or context to determine whether a specified criterion holds.
Clojure: The Essential Reference
A predicate is a function whose result is interpreted as a boolean condition, even when its returned value is not literally boolean.
- How it is used
- Uses predicates to select collection items, answer all-or-any questions, compose checks, and enforce function conditions.
- How deep it goes
- Defines the unary contract and truth-value interpretation, then details return values, short-circuiting, laziness, and assertion failures.
- Examples
- Demonstrates odd-number filtering, palindrome checks, email spam detection, prize lookup, and validation before and after saving an item.
- What you can do after
- Apply it via Clojure's filter, remove, every?, some, every-pred, and some-fn to select values and combine checks.
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Kafka Streams in Action, Second Edition
Predicate is a boolean-valued functional interface that evaluates a record to determine whether it belongs in a branch.
- How it is used
- Routes Kafka Streams records through filters, branches, and data-driven aggregation decisions.
- How deep it goes
- Explains predicate use through filter and split APIs, then shows Processor API tests without detailing predicate internals.
- Examples
- Uses reward-qualifying purchases, coffee and electronics routing, and sensor-driven aggregation.
- What you can do after
- Apply it via Kafka Streams to retain, drop, route, or aggregate records by record-level conditions.
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Learn SQL in a Month of Lunches
A predicate is a Boolean SQL expression that evaluates whether a condition holds for data involved in a query operation.
- How it is used
- Uses predicates to join related tables, filter query results, and limit multitable updates.
- How deep it goes
- Defines true, false, and unknown evaluation, then demonstrates join, filter, and multitable-update predicate placement without formal evaluation internals.
- Examples
- Demonstrates matching orderheader to customer for order 1001 and changing prices of titles linked to AuthorID 12.
- What you can do after
- Apply predicates to match table rows, restrict results, and recognize product-specific multitable UPDATE syntax.
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Kotlin in Action, 2E
A predicate function is a function that evaluates an input and returns a Boolean indicating whether it satisfies a condition.
- How it is used
- Uses Boolean-returning functions to query, filter, and validate elements in collections and sequences.
- How deep it goes
- Explains predicate syntax, collection behavior, higher-order implementation, negation choices, and empty-collection edge cases.
- Examples
- Demonstrates age checks, collection queries, character filtering, empty collections, and configurable contact-list filtering.
- What you can do after
- Apply predicates via Kotlin collection functions and implement higher-order functions that accept or return filtering logic.
100 C++ Mistakes and How to Avoid Them
A predicate is a Boolean-valued function that determines whether a value satisfies a condition.
- How it is used
- Uses predicates to retain or reject values in ranges and to express Boolean tests directly.
- How deep it goes
- Defines predicates, demonstrates filtering, and refactors a verbose Boolean implementation without descending into internals.
- Examples
- Uses even-number testing, absolute-value transformation, range filtering, and accumulation over retained values.
- What you can do after
- Apply it via std::views::filter and write concise functions that return computed Boolean results directly.
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Related concepts
- filteringused by · Filtering is the operation of selecting or excluding items from data or a collection according to specified criteria.
- functionkind of · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
- booleanproduces · A Boolean is a logical type or value representing truth or falsity, conventionally with two states: true and false.
- KStream.splitused by · KStream.split is a Kafka Streams DSL method that begins branching a KStream and returns a BranchedKStream.
- BranchedKStream.branchused by · BranchedKStream.branch is a Kafka Streams method that creates a branch by applying a predicate and branch-processing definition to records.
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