第三章陣列的使用

第三章陣列的使用 鄧姚文 joseph.deng@gmail.com http://www.ywdeng.idv.tw

大綱 • 何謂陣列 • 關連式陣列 • 陣列排序 • 數值索引陣列 • 多維陣列

何謂陣列 • 連續資料的集合 • 透過索引或 key 存取

數值索引陣列 • $products = array(“Tires”, “Oil”, “Spark Plugs”); • array() 是一個程式結構，不是函式 • $products[0] 即 “Tires” • $products[1] 即 “Oil” • $products[2] 即 “Spark Plugs” • for ($i = 0; $i < 3; $i++)echo “$products[$i]”; • 可以隨時增加元素 • $products[3] = “Fuses”;

range • Create an array containing a range of elements • array range ( int low, int high [, int step])

<?php // array(0,1,2,3,4,5,6,7,8,9) foreach(range(0, 9) as $number) { echo $number; } // The step parameter was introduced in 5.0.0 // array(0,10,20,30,40,50,60,70,80,90,100) foreach(range(0, 100, 10) as $number) { echo $number; } // Use of characters introduced in 4.1.0 // array('a','b','c','d','e','f','g','h','i'); foreach(range('a', 'i') as $letter) { echo $letter; } // array('c','b','a'); foreach(range('c', 'a') as $letter) { echo $letter; } ?>

關連式陣列 • $prices = array(“Tires” => 100,“Oil” => 10, “Spark Plugs” => 4); • $prices[“Tires”] 即 100 • 在迴圈中使用 each() 和 list() 存取陣列元素 • each : Return the current key and value pair from an array and advance the array cursor • If the internal pointer for the array points past the end of the array contents, each() returns FALSE. • List : Assign variables as if they were an array • list() only works on numerical arrays and assumes the numerical indices start at 0.

$prices = array("Tires"=>100,"Oil"=>10,"Spark Plugs"=>4); $prices = array("Tires"=>100); $prices["Oil"] = 10; $prices["Spark Plugs"] = 4; while ($element = each($prices)) { echo $element["key"]; echo "-"; echo $element["value"]; echo "<br>"; } reset($prices); while (list($product, $price) = each($prices)) { echo "$product - $price <br>"; }

多維陣列 • $products = array(array(“TIR”, “Tires”, 100),array(“OIL”, “Oil”, 10),array(“SPK”, “Spark Plugs”, 4)); • $product[0][0] 即 “TIR”

陣列排序 • 數值索引陣列 • sort() 升冪（從小到大）排序 • 關連式陣列 • asort() • Sort an array and maintain index association • ksort() • Sort an array by key • 逆向排序（降冪，從大到小） • rsort()、arsort()、krsort()

$fruits = array ("d"=>"lemon", "a"=>"orange", "b"=>"banana", "c"=>"apple"); asort ($fruits); reset ($fruits); while (list ($key, $val) = each ($fruits)) { echo "$key = $val\n"; } This example would display: c = apple b = banana d = lemon a = orange

$fruits = array ("d"=>"lemon", "a"=>"orange", "b"=>"banana", "c"=>"apple"); ksort ($fruits); reset ($fruits); while (list ($key, $val) = each ($fruits)) { echo "$key = $val\n"; } This example would display: a = orange b = banana c = apple d = lemon

在多維陣列中排序 • 自行定義物件比較大小的方式，把多維陣列當作物件的一維陣列排序 • 自行定義物件比較大小的函式，傳入參數：兩個物件，傳回值： • =0 兩個物件相等 • >0 第一個物件比較大 • <0 第二個物件比較大 • void usort ( array array, callback cmp_function) • Sort an array by values using a user-defined comparison function • 逆向使用者自訂排序 • kusort()

function cmp ($a, $b) { if ($a == $b) return 0; return ($a > $b) ? -1 : 1; } $a = array (3, 2, 5, 6, 1); usort ($a, "cmp"); while (list ($key, $value) = each ($a)) { echo "$key: $value\n"; } This example would display: 0: 6 1: 5 2: 3 3: 2 4: 1

對陣列重新排序 • shuffle() 亂排 • This function shuffles (randomizes the order of the elements in) an array. • You must use srand() to seed this function. • Example: http://w3.im.knu.edu.tw/~annie/chapter03/bobs_front_page.php

相反的順序 • array_reverse -- Return an array with elements in reverse order • array array_reverse ( array array [, bool preserve_keys]) • array_reverse() takes input array and returns a new array with the order of the elements reversed, preserving the keys if preserve_keys is TRUE. $input = array ("php", 4.0, array ("green", "red")); $result = array_reverse ($input); $result_keyed = array_reverse ($input, TRUE);

Array ( [0] => Array ( [0] => green [1] => red ) [1] => 4 [2] => php ) Array ( [2] => Array ( [0] => green [1] => red ) [1] => 4 [0] => php ) This makes both $result and $result_keyed have the same elements, but note the difference between the keys. The printout of $result and $result_keyed will be:

由檔案載入陣列範例：vieworders.php • file -- Reads entire file into an array • array file ( string filename [, int use_include_path [, resource context]]) • Identical to readfile(), except that file() returns the file in an array. Each element of the array corresponds to a line in the file, with the newline still attached. Upon failure, file() returns FALSE.

由檔案載入陣列範例：vieworders2.php • explode -- Split a string by string • array explode ( string separator, string string [, int limit]) • Returns an array of strings, each of which is a substring of string formed by splitting it on boundaries formed by the string separator. If limit is set, the returned array will contain a maximum of limit elements with the last element containing the rest of string. • If separator is an empty string (""), explode() will return FALSE. If separator contains a value that is not contained in string, then explode() will return an array containing string. • intval -- Get integer value of a variable • int intval ( mixed var [, int base])

其他陣列操作 • each() -- Return the current key and value pair from an array and advance the array cursor • next() -- Advance the internal array pointer of an array • prev() -- Rewind the internal array pointer • current() -- Return the current element in an array • end() -- Set the internal pointer of an array to its last element • reset() -- Set the internal pointer of an array to its first element

對陣列中每一個元素逐一進行運算 • array_walk -- Apply a user function to every member of an array • int array_walk ( array array, callback function [, mixed userdata])

<?php $fruits = array ("d"=>"lemon", "a"=>"orange", "b"=>"banana", "c"=>"apple"); function test_alter (&$item1, $key, $prefix) { $item1 = "$prefix: $item1"; } function test_print ($item2, $key) { echo "$key. $item2<br>\n"; } echo "Before ...:\n"; array_walk ($fruits, 'test_print'); array_walk ($fruits, 'test_alter', 'fruit'); echo "... and after:\n"; array_walk ($fruits, 'test_print'); ?>

The printout of the program above will be: Before ...: d. lemon a. orange b. banana c. apple ... and after: d. fruit: lemon a. fruit: orange b. fruit: banana c. fruit: apple

計算陣列元素個數 • count -- Count elements in a variable • int count ( mixed var) • Returns the number of elements in var, which is typically an array (since anything else will have one element). • If var is not an array, 1 will be returned (exception: count(NULL) equals 0). • sizeof -- Alias of count() • array_count_values -- Counts all the values of an array • array array_count_values ( array input) • array_count_values() returns an array using the values of the input array as keys and their frequency in input as values.

將陣列轉純量變數 • extract -- Import variables into the current symbol table from an array • int extract ( array var_array [, int extract_type [, string prefix]]) • This function is used to import variables from an array into the current symbol table. It takes an associative array var_array and treats keys as variable names and values as variable values. For each key/value pair it will create a variable in the current symbol table, subject to extract_type and prefix parameters. • extract() checks each key to see whether it has a valid variable name. It also checks for collisions with existing variables in the symbol table. The way invalid/numeric keys and collisions are treated is determined by the extract_type. It can be one of the following values:

將陣列轉純量變數 • EXTR_OVERWRITE（default） • If there is a collision, overwrite the existing variable. • EXTR_SKIP • If there is a collision, don't overwrite the existing variable. • EXTR_PREFIX_SAME • If there is a collision, prefix the variable name with prefix. • EXTR_PREFIX_ALL • Prefix all variable names with prefix. Beginning with PHP 4.0.5, this includes numeric variables as well. • EXTR_PREFIX_INVALID • Only prefix invalid/numeric variable names with prefix. This flag was added in PHP 4.0.5. • EXTR_IF_EXISTS • Only overwrite the variable if it already exists in the current symbol table, otherwise do nothing. This is useful for defining a list of valid variables and then extracting only those variables you have defined out of $_REQUEST, for example. This flag was added in PHP 4.2.0. • EXTR_PREFIX_IF_EXISTS • Only create prefixed variable names if the non-prefixed version of the same variable exists in the current symbol table. This flag was added in PHP 4.2.0. • EXTR_REFS • Extracts variables as references. This effectively means that the values of the imported variables are still referencing the values of the var_array parameter. You can use this flag on its own or combine it with any other flag by OR'ing the extract_type. This flag was added in PHP 4.3.0.

第三章 陣列的使用