平行数组
平行数组是程序设计采用多个数组隐式表示一个以记录(record)为元素的数组。多个数组在同一下标的元素隐式对应于记录的各个域。
例子[编辑]
例如,可以声明一个数组包含100个名字,另一个数组包含100个年龄(整型),相同下标的元素成对表示一个人:
int ages[] = {0, 17, 2, 52, 25}; char *names[] = {"None", "Mike", "Billy", "Tom", "Stan"}; int parent[] = {0 /*None*/, 3 /*Tom*/, 1 /*Mike*/, 0 /*None*/, 3 /*Tom*/}; for(i = 1; i <= 4; i++) { printf("Name: %s, Age: %d, Parent: %s \n", names[i], ages[i], names[parent[i]]); }
Perl语言:
my %data = ( first_name => ['Joe', 'Bob', 'Frank', 'Hans' ], last_name => ['Smith','Seger','Sinatra','Schultze'], height_in_cm => [169, 158, 201, 199 ]); for $i (0..$#{$data{first_name}}) { printf "Name: %s %s\n", $data{first_name}[$i], $data{last_name}[$i]; printf "Height in CM: %i\n", $data{height_in_cm}[$i]; }
first_names = ['Joe', 'Bob', 'Frank', 'Hans' ] last_names = ['Smith','Seger','Sinatra','Schultze'] heights_in_cm = [169, 158, 201, 199 ] for i in range(len(first_names)): print "Name: %s %s" % (first_names[i], last_names[i]) print "Height in CM: %s" % heights_in_cm[i] # Using zip: for first_name, last_name, height in zip(first_names, last_names, heights_in_cm): print "Name: %s %s" % (first_name, last_name) print "Height in CM: %s" % height_in_cm
优点与缺点[编辑]
优点:
- 可用于仅支持基本类型作为数组元素类型的那些编程语言
- 易于理解使用
- 可能会避免了内存对齐从而节省了内存占用。
- 顺序遍历小数组有利于提高cache一致性。
- 有利于使用SIMD指令。
缺点:
- 使用多个域时不利于cache性能
- 增加或删除元素时代价高昂。
参见[编辑]
参考文献[编辑]
- Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. Introduction to Algorithms, Second Edition. MIT Press and McGraw-Hill, 2001. ISBN 0-262-03293-7. Page 209 of section 10.3: Implementing pointers and objects.
- Skeet, Jon. Anti-pattern: parallel collections. 2014-06-03 [2014-10-28]. (原始内容存档于2014-10-28).