Aggregate pattern: Difference between revisions

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{{Short description|Concepts in statistics and computer science}}

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{{one source |date=March 2024}}

An '''Aggregate pattern''' can refer to concepts in either statistics or computer programming. Both uses dealsimplify withcomplexity considering a large case as composed ofinto smaller, simpler, piecesparts.

== Statistics ==

An aggregate pattern is an important statistical concept in many fields that rely on [[statistics]] to predict the behavior of large groups, based on the tendencies of subgroups to consistently behave in a certain way. It is particularly useful in [[sociology]], [[economics]], [[psychology]], and [[criminology]].

== Computer programming ==

In ''[[Design Patterns]]'', an aggregate is not a [[Software design pattern|design pattern]] but rather refers to an object such as a list, vector, or generator which provides an interface for creating [[iterator]]s. The following example code is in [[Python (programming language)|Python]].

{{Expand-section|a clear explanation of the code example or adding another code example|date=October 2007}}

<syntaxhighlight lang="python">

def fibonacci(n: int):

a, b = 0, 1

count = 0

while count < n:

count += 1

a, b = b, a + b

yield a

for x in fibonacci(10):

In [[computer programming]], an aggregate pattern is a [[design pattern (computer science)|design pattern]].

print(x)

def fibsum(n: int) -> int:

Members of a common [[Subclass (computer science)|subclass]] are each known to have certain [[Method (computer science)|method]]s. These methods return information about the state of that particular [[object (computer science)|object]]. Sometimes an application is concerned with an aggregation, or amalgamation, of data from several objects of the same type. This leads to redundant code in various places throughout the program:

total = 0

for x in fibonacci(n):

total += x

return 1;total

def fibsum_alt(n: int) -> int:

(Perl example)

"""

<source lang="perl">

Alternate implementation. demonstration that Python's built-in function sum()

my $subtotal;

works with arbitrary iterators.

foreach my $item (@cart) {

"""

$subtotal += $item->query_price();

return sum(fibonacci(n))

}

my $weight;

foreach my $item (@cart) {

$weight += $item->query_weight();

}

# and so on

</source>

myNumbers = [1, 7, 4, 3, 22]

Aggregation uses a [[wrapper pattern|wrapper]] to encapsulate as much duplicate functionality across methods as possible:

def average(g) -> float:

<source lang="perl">

return float(sum(g)) / len(g) # In Python 3 the cast to float is no longer be necessary

package Cart::Basket;

</syntaxhighlight>

Python hides essentially all of the details using the [https://docs.python.org/3/library/stdtypes.html#iterator-types iterator protocol]. Confusingly, ''[[Design Patterns]]'' uses "aggregate" to refer to the blank in the code <code>for x in ___:</code> which is unrelated to the term "aggregation".<ref>[[Design Patterns]], p. 22: "Aggregation implies that one object owns or is responsible for another object. ... Aggregation implies that an aggregate object and its owner have identical lifetimes."</ref> Neither of these terms refer to the statistical aggregation of data such as the act of adding up the Fibonacci sequence or taking the average of a list of numbers.

@ISA = qw(Cart::Item);

sub query_price {

my $self = shift;

my $contents = $self->{contents};

foreach my $item (@$contents) {

}

}

# other query_ routines here...

sub add_item {

my $self = shift;

my $contents = $self->{contents};

my $item = shift; $item->isa('Cart::Item') or die;

push @$contents, $item;

return 1;

}

</source>

Aggregation is like iteration in that they both present information gleaned from a number of objects through a tidy interface in one object.

== See also ==

* [[Visitor pattern]]

* [[Template class]]

Line 64 ⟶ 47:

* [[Type safety]]

* [[Functional programming]]

== References ==

{{Reflist}}

[[Category:Software design patterns]]

[[Category:Articles with example PerlPython (programming language) code]]

{{statistics-stub}}