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

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];
}

Python语言:

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

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

参考文献
  • 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. . 2014-06-03 [2014-10-28]. （原始内容存档于2014-10-28）.
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