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Specifically I've seen it used in the context of text filtering. As if "predicate" == "filter criteria".

Is this accurate?

ack
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7 Answers7

169

A predicate ('PRED-i-cat') is the part of a sentence that contains the verb and tells you something about the subject.

For instance, in the sentence

"Mike is eating", we have the subject, 'Mike', and the predicate, 'is eating'.

In the context of computer science, we aren't interested in stating a fact, but rather, in testing a true/false condition for the purpose of deciding whether to do something.

Person mike;

if (!mike.isEating())
    feedPerson(mike);

The isEating() member of mike (an instance of Person) is a predicate. It returns true or false for the assertion that the person (mike in this case) is eating. The predicate is being used to decide whether or not to feed the person.

Predicates are often found in the form of callbacks, but in general we can use the term for any function that returns a bool based on evaluation of the truth of an assertion.

For sorting, might want have the member function

bool Fruit::ComesAfter(Fruit x) ...

as our predicate. If x comes after us, our sorting algorithm will swap the two fruits.

There's also the term predicate (predi-KATE). In English we use it like this:

"Graduation is predicated upon attainment of passing grades."

It means one thing depends on another.

In computer science, we use this form of the word to describe conditional execution.

For instance, in CUDA programming, there are assembly instructions whose execution we can predicate (KATE) on a prior result. That is, you set a predicate (CAT) flag that, if true, causes the instruction to be executed, and if false, causes the instruction to be treated as a NOP. Thus the execution of the instruction is predicated upon the indicated predicate flag.

The uses are very similar.

starball
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cwm9
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111

It is a term most commonly used in the field of Mathematical Logic.

From wikipedia

In mathematics, a predicate is either a relation or the boolean-valued function that amounts to the characteristic function or the indicator function of such a relation.

A function P: X→ {true, false} is called a predicate on X. When P is a predicate on X, we sometimes say P is a property of X.

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"predicate" == "filter criteria"

Community
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Prasoon Saurav
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  • I would change "to some extent" to "exactly the same", since one can either filter an element or not, which implies a boolean function, i.e. a predicate. – Dimitris Andreou Jul 24 '10 at 17:25
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    This is used in computer science, both in theory and in programming practice. A predicate as a function that get an arguments, and returns a boolean. it returns true if the argument *matchs the predicate* i.e. the function name-filter. Example: isBlue(arg), here Java predicate interface --> https://docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html – Hernán Eche Oct 07 '15 at 18:40
44

The word comes from logic.

A predicate is an "is" boolean question about the inputs.

"IsNull" is a predicate question.

Also, wikipedia link about Predicates in Math.

Paul Nathan
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23

A predicate is a statement about something that is either true or false.

user207421
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Bradley
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  • @user1907906 The 'I would describe' part is just fluff, but the remainder certainly constitutes an answer. There is no critique or clarification request here. – user207421 Sep 07 '15 at 10:36
11

Just to simplify things . predicate is a function that return a true or false value based on some condition.

it's used as a "filter criteria" meaning lets consider an array of numbers and a predicate that returns true if number > 0 , false other wise .

function predicate(number){
  return number > 0 
}
// array of numbers 
var numbers = [-2 , -1 , 0 , 1 , 2];

var newNumbers = numbers.filter(predicate);

// newNumbers => [1 , 2] ;

filter is a function that returns a new array based on a predicate ( or a "filter criteria". )

it has filtered the array based on the value of predicate

  • true : include value
  • false : don't include it
Ahmed Eid
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8

Proposition:

  • either definitely set to true or false
  • not dependent on values of the parameters
  • e.g.
    • "x+2=2x, when x = -2" => true
    • "2*2=5" => false

Predicate:

  • truth value depends on the parameter's value
  • e.g.
    • "x+2=2x" => truth value is unknown and is dependent on the value of x

Use quantifiers to transform predicate to proposition:

  • ∃x∈Z (x+2=2x) "There exists a x in the set of integers such that x+2=2x"
JeanieJ
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Predicate is a function that takes one element as input parameter and return either true or false. Predicates are used in higher order functions, applied to a given function(a.k.a transformer) element-wise to a list of elements and returns a list of results. Transformer is a function applies to each element and will produce one or more new elements.

Remario
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