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documentation of array_filter, array_map, and array_reduce

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@44368 c90b9560-bf6c-de11-be94-00142212c4b1
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Jesus M. Castagnetto 2001-03-27 12:57:19 +00:00
parent afdabfca5d
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296
functions/array.xml
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@ -200,6 +200,62 @@ $result = array_diff ($array1, $array2);
</refsect1>
</refentry>
<refentry id="function.array-filter">
<refnamediv>
<refname>array_filter</refname>
<refpurpose>Filters elements of an array using a callback function</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>array <function>array_filter</function></funcdef>
<paramdef>array <parameter>input</parameter></paramdef>
<paramdef>mixed
<parameter><optional>callback</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<para>
<function>Array_filter</function> returns an array
containing all the elements of <parameter>input</parameter>
filtered according a callback function. If the
<parameter>input</parameter> is an associative array
the keys are preserved.
</para>
<para>
<example>
<title><function>Array_filter</function> example</title>
<programlisting role="php">
function odd($var) {
return ($var % 2 == 1);
}
function even($var) {
return ($var % 2 == 0);
}
$array1 = array ("a"=&gt;1, "b"=&gt;2, "c"=&gt;3, "d"=&gt;4, "e"=&gt;5);
$array2 = array (6, 7, 8, 9, 10, 11, 12);
$odd_arr = array_filter($array1, "odd");
$even_arr = array_filter($array2, "even");
</programlisting>
</example>
</para>
<para>
This makes <varname>$odd_arr</varname> have
<literal>array ("a"=&gt;1, "c"=&gt;3, "e"=&gt;5);</literal>,
and <varname>$even_arr</varname> have
<literal>array (6, 8, 10, 12);</literal>,
</para>
<para>
See also <function>array_map</function>,
<function>array_reduce</function>.
</para>
</refsect1>
</refentry>
<refentry id="function.array-flip">
<refnamediv>
<refname>array_flip</refname>
@ -342,6 +398,184 @@ function array_keys ($arr, $term="") {
</refsect1>
</refentry>
<refentry id="function.array-map">
<refnamediv>
<refname>array_map</refname>
<refpurpose>Applies the callback to the elements of the given arrays</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>array <function>array_map</function></funcdef>
<paramdef>mixed <parameter>callback</parameter></paramdef>
<paramdef>array <parameter>arr1</parameter></paramdef>
<paramdef>array
<parameter><optional>arr2...</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<para>
<function>Array_map</function> returns an array
containing all the elements of <parameter>arr1</parameter>
after applying the callback function to each one.
The number of parameters that the callback function accepts should
match the number of arrays passed to the <function>array_map</function>
</para>
<para>
<example>
<title><function>Array_map</function> example</title>
<programlisting role="php">
function cube($n) {
return $n*$n*$n;
}
$a = array(1, 2, 3, 4, 5);
$b = array_map("cube", $a);
</programlisting>
</example>
</para>
<para>
This will result in <varname>$b</varname> containing
<literal>array (1, 8, 27, 64, 125);</literal>
</para>
<para>
<example>
<title><function>Array_filter</function> - using more arrays</title>
<programlisting role="php">
function show_Spanish($n, $m) {
return "The number $n is called $m in Spanish";
}
function map_Spanish($n, $m) {
return array ($n => $m);
}
$a = array(1, 2, 3, 4, 5);
$b = array("uno", "dos", "tres", "cuatro", "cinco");
$c = array_map("show_Spanish", $a, $b);
print_r($c);
// will output:
// Array
// (
// [0] => The number 1 is called uno in Spanish
// [1] => The number 2 is called dos in Spanish
// [2] => The number 3 is called tres in Spanish
// [3] => The number 4 is called cuatro in Spanish
// [4] => The number 5 is called cinco in Spanish
// )
$d = array_map("map_Spanish", $a , $b);
print_r($d);
// will output:
// Array
// (
// [0] => Array
// (
// [1] => uno
// )
//
// [1] => Array
// (
// [2] => dos
// )
//
// [2] => Array
// (
// [3] => tres
// )
//
// [3] => Array
// (
// [4] => cuatro
// )
//
// [4] => Array
// (
// [5] => cinco
// )
//
// )
</programlisting>
</example>
</para>
<para>
Usually when using two or more arrays, they should be of equal length
because the callback function is applied in parallel to the corresponding
elements.
If the arrays are of unequal length, the shortest one will be extended
with empty elements.
</para>
<para>
An interesting use of this function is to construct an array of arrays,
which can be easily performed by using <literal>null</literal>
as the name of the callback function
</para>
<para>
<example>
<title><function>Array_map</function> - creating an array of arrays</title>
<programlisting role="php">
$a = array(1, 2, 3, 4, 5);
$b = array("one", "two", "three", "four", "five");
$c = array("uno", "dos", "tres", "cuatro", "cinco");
$d = array_map(null, $a, $b, $c);
print_r($d);
// will output:
// Array
// (
// [0] => Array
// (
// [0] => 1
// [1] => one
// [2] => uno
// )
//
// [1] => Array
// (
// [0] => 2
// [1] => two
// [2] => dos
// )
//
// [2] => Array
// (
// [0] => 3
// [1] => three
// [2] => tres
// )
//
// [3] => Array
// (
// [0] => 4
// [1] => four
// [2] => cuatro
// )
//
// [4] => Array
// (
// [0] => 5
// [1] => five
// [2] => cinco
// )
//
// )
</programlisting>
</example>
</para>
<para>
See also <function>array_filter</function>,
<function>array_reduce</function>.
</para>
</refsect1>
</refentry>
<refentry id="function.array-merge">
<refnamediv>
<refname>array_merge</refname>
@ -790,6 +1024,68 @@ $result_keyed = array_reverse ($input, TRUE);
</refsect1>
</refentry>
<refentry id="function.array-reduce">
<refnamediv>
<refname>array_reduce</refname>
<refpurpose>
Iteratively reduce the array to a single value using a callback function
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<funcsynopsis>
<funcprototype>
<funcdef>mixed <function>array_reduce</function></funcdef>
<paramdef>array <parameter>input</parameter></paramdef>
<paramdef>mixed <parameter>callback</parameter></paramdef>
<paramdef>int
<parameter><optional>initial</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<para>
<function>Array_reduce</function> applies iteratively the
<parameter>callback</parameter> function to the elements of the
array <parameter>input</parameter>, so as to reduce the array to
a single value. If the optional <parameter>intial</parameter> is
avaliable, it will be used at the beginning of the process, or as
a final result in case the array is empty.
</para>
<para>
<example>
<title><function>Array_reduce</function> example</title>
<programlisting role="php">
function rsum($v, $w) {
$v += $w;
return $v;
}
function rmul($v, $w) {
$v *= $w;
return $v;
}
$a = array(1, 2, 3, 4, 5);
$x = array();
$b = array_reduce($a, "rsum");
$c = array_reduce($a, "rmul", 10);
$d = array_reduce($x, "rsum", 1);
</programlisting>
</example>
</para>
<para>
This will result in <varname>$b</varname> containing
<literal>15</literal>, <varname>$c</varname> containing
<literal>1200</literal> (= 1*2*3*4*5*10), and <varname>$d</varname>
containing <literal>1</literal>.
</para>
<para>
See also <function>array_filter</function>,
<function>array_map</function>.
</para>
</refsect1>
</refentry>
<refentry id="function.array-shift">
<refnamediv>
<refname>array_shift</refname>