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遍历
array
数组中的每个值，并将每个值传递给
callback
回调函数。
如果
callback
回调函数返回
true
，则将
array
数组中的当前值返回到结果
array
数组中。
返回结果
array
数组的键名（下标）会维持不变，如果
array
参数是索引数组，返回的结果
array
数组键名（下标）可能会不连续。
可以使用
array_values()
函数对数组重新索引。
示例 #1
array_filter()
示例
<?php
function
odd
(
$var
)
{
// 返回输入整数是否为奇数（单数）
return
$var
&
1
;
}
function
even
(
$var
)
{
// 返回输入整数是否为偶数
return !(
$var
&
1
);
}
$array1
= [
'a'
=>
1
,
'b'
=>
2
,
'c'
=>
3
,
'd'
=>
4
,
'e'
=>
5
];
$array2
= [
6
,
7
,
8
,
9
,
10
,
11
,
12
];
echo
"Odd :\n"
;
print_r
(
array_filter
(
$array1
,
"odd"
));
echo
"Even:\n"
;
print_r
(
array_filter
(
$array2
,
"even"
));
?>
Odd :
Array
[a] => 1
[c] => 3
[e] => 5
Even:
Array
[0] => 6
[2] => 8
[4] => 10
[6] => 12
示例 #2
array_filter()
不使用
callback
参数时
<?php
$entry
= [
0
=>
'foo'
,
1
=>
false
,
2
=> -
1
,
3
=>
null
,
4
=>
''
,
5
=>
'0'
,
6
=>
0
,
];
print_r
(
array_filter
(
$entry
));
?>
Array
[0] => foo
[2] => -1
示例 #3
array_filter()
不使用
mode
参数时
<?php
$arr
= [
'a'
=>
1
,
'b'
=>
2
,
'c'
=>
3
,
'd'
=>
4
];
var_dump
(
array_filter
(
$arr
, function(
$k
) {
return
$k
==
'b'
;
},
ARRAY_FILTER_USE_KEY
));
var_dump
(
array_filter
(
$arr
, function(
$v
,
$k
) {
return
$k
==
'b'
||
$v
==
4
;
},
ARRAY_FILTER_USE_BOTH
));
?>
array(1) {
["b"]=>
int(2)
array(2) {
["b"]=>
int(2)
["d"]=>
int(4)
array_intersect()
- 计算数组的交集
array_map()
- 为数组的每个元素应用回调函数
array_reduce()
- 用回调函数迭代地将数组简化为单一的值
array_walk()
- 使用用户自定义函数对数组中的每个元素做回调处理
Niko E
¶
11 months ago
Note that a filtered array no longer encodes to json arrays, as the indices are no longer continuous:
$a = ['a', 'b', 'c'];
var_dump(json_encode($a)); // ["a","b","c"]
$a = array_filter($a, function ($x) { return $x == 'b'; });
var_dump(json_encode($a)); // {"1": "b"}
you can use array_values get a continuous array
var_dump(json_encode(array_values($a))); // ["b"]
nicolaj dot knudsen at gmail dot com
¶
6 years ago
If you like me have some trouble understanding example #1 due to the bitwise operator (&) used, here is an explanation.
The part in question is this callback function:
<?php
function
odd
(
$var
)
{
return(
$var
&
1
);
}
?>
If given an integer this function returns the integer 1 if $var is odd and the integer 0 if $var is even.
The single ampersand, &, is the bitwise AND operator. The way it works is that it takes the binary representation of the two arguments and compare them bit for bit using AND. If $var = 45, then since 45 in binary is 101101 the operation looks like this:
45 in binary: 101101
1 in binary: 000001
------
result: 000001
Only if the last bit in the binary representation of $var is changed to zero (meaning that the value is even) will the result change to 000000, which is the representation of zero.
TechNyquist
¶
1 year ago
Keep in mind that, as of PHP 7.4 and above, you can use arrow functions to as argument.
So for example if you want to leave values bigger than 10:
<?php
$arr
=
array_filter
(
$numbers
,
fn
(
$n
) =>
$n
>
10
);
?>
also, combine with key-flag to cut certain keys:
<?php
$arr
=
array_filter
(
$entries
,
fn
(
$key
) => !
in_array
(
$key
, [
'key1'
,
'key5'
]),
ARRAY_FILTER_USE_KEY
);
?>
and so on.
marc dot vanwoerkom at fernuni-hagen dot de
¶
19 years ago
Some of PHP's array functions play a prominent role in so called functional programming languages, where they show up under a slightly different name:
<?php
array_filter
() ->
filter
(),
array_map
() ->
map
(),
array_reduce
() ->
foldl
() (
"fold left"
)
?>
Functional programming is a paradigm which centers around the side-effect free evaluation of functions. A program execution is a call of a function, which in turn might be defined by many other functions. One idea is to use functions to create special purpose functions from other functions.
The array functions mentioned above allow you compose new functions on arrays.
E.g. array_sum = array_map("sum", $arr).
This leads to a style of programming that looks much like algebra, e.g. the Bird/Meertens formalism.
E.g. a mathematician might state
map(f o g) = map(f) o map(g)
the so called "loop fusion" law.
Many functions on arrays can be created by the use of the foldr() function (which works like foldl, but eating up array elements from the right).
I can't get into detail here, I just wanted to provide a hint about where this stuff also shows up and the theory behind it.
ASchmidt at Anamera dot net
¶
2 years ago
Depending on the intended meanings of your "empty" array values, e.g., null and empty string, vs. an integer 0 or a boolean false, be mindful of the result of different filters.
<?php
declare(
strict_types
=
1
);
$array
= array(
'null'
=>
null
,
'nullstring'
=>
''
,
'intzero'
=>
0
,
'stringzero'
=>
'0'
,
'false'
=>
false
,
'stringfalse'
=>
'false'
, );
$filtered1
=
array_filter
(
$array
,
'strlen'
);
$filtered2
=
array_filter
(
$array
, function(
$v
) { return !
is_null
(
$v
); } );
$filtered3
=
array_filter
(
$array
, function(
$v
) { return !(
is_null
(
$v
) or
''
===
$v
); } );
var_dump
(
$array
,
$filtered1
,
$filtered2
,
$filtered3
);
?>
Results in:
array (size=3)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'stringfalse' => string 'false' (length=5)
array (size=5)
'nullstring' => string '' (length=0)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'false' => boolean false
'stringfalse' => string 'false' (length=5)
array (size=4)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'false' => boolean false
'stringfalse' => string 'false' (length=5)
marc dot gray at gmail dot com
¶
9 years ago
My favourite use of this function is converting a string to an array, trimming each line and removing empty lines:
<?php
$array
=
array_filter
(
array_map
(
'trim'
,
explode
(
"\n"
,
$string
)),
'strlen'
);
?>
Although it states clearly that array keys are preserved, it's important to note this includes numerically indexed arrays. You can't use a for loop on $array above without processing it through array_values() first.
Hayley Watson
¶
1 month ago
The fact that array_filter preserves keys makes partitioning an array into [elements that pass the test, elements that fail the test] quite easy. In essence:
<?php
function
partition
(
$array
,
$test
)
{
$pass
=
array_filter
(
$array
,
$test
);
$fail
=
array_diff_key
(
$array
,
$pass
);
return [
false
=>
$fail
,
true
=>
$pass
];
}
?>
The array_diff_key call is key; indexing the returned array as shown allows lines like "$failures = $partition[false];" to do the right thing (the booleans get converted to integers of course, but it's consistent and self-documenting).
justinphiggs at gmail dot com
¶
1 year ago
Check if all elements in array are not empty/null/falsy.
------------------------------
Supposing you have a one dimensional array...
<?php
$spicy_numbers
= [
69
,
420
,
ɸ
];
?>
And you want to easily check that all elements in said array are not null/empty/any falsy value, instead of running a loop over each element, you can pass the array to
<?php array_filter
()
?>
, with no callback function, and then check if the returned array is the same size as the original, since
<?php array_filter
()
?>
strips out all non-truthy values including 0 when no callback is provided.
Example:
<?php
$spicy_numbers
= [
69
,
420
,
''
];
if (
count
(
array_filter
(
$spicy_numbers
) ) !==
count
(
$spicy_numbers
) ) {
} else {
}
?>
As a neat little function, you could do this:
<?php
function
is_array_full
(
$arr
) {
$array_count
=
count
(
$arr
);
$filtered_count
=
count
(
array_filter
(
$arr
) );
return (
$array_count
===
$filtered_count
) ?
true
:
false
;
}
?>
