获取多维数组中特定列的所有值

I have a multidimensional array, that has say, x number of columns and y number of rows.

我有一个多维数组，它有x列数和y行数。

I want specifically all the values in the 3rd column.

我特别想要第三列中的所有值。

The obvious way to go about doing this is to put this in a for loop like this

做这个的最明显的方法是像这样把它放到一个for循环中

for(i=0;i<y-1;i++)
{
   $ThirdColumn[] = $array[$i][3];
}

but there is an obvious time complexity of O(n) involved here. Is there a built in way for me to simply extract each of these rows from the array without having to loop in.

但是这里显然涉及到O(n)的时间复杂度。是否有一个内置的方法可以让我简单地从数组中提取这些行，而不必循环。

For example (this does not work offcourse)

例如(这在正常情况下是行不通的)

$ThirdColumn  = $array[][3]

5 个解决方案

#1

Given a bidimensional array $channels:

给定一个二维数组$channels:

$channels = array(
    array(
        'id' => 100,
        'name' => 'Direct'
    ),
    array(
        'id' => 200,
        'name' => 'Dynamic'
    )
);

A nice way is using array_map:

一个很好的方法是使用array_map:

$_currentChannels = array_map(function ($value) {
    return  $value['name'];
}, $channels);

and if you are a potentate (php 5.5+) through array_column:

如果你是通过array_column的potentate (php 5.5+):

$_currentChannels = array_column($channels, 'name');

Both results in:

这两个结果:

Array
(
    [0] => Direct
    [1] => Dynamic
)

Star guests: array_map (php4+) and array_column (php5.5+)

明星嘉宾:array_map (php4+)和array_column (php5.5+)

// array array_map ( callable $callback , array $array1 [, array $... ] )
// array array_column ( array $array , mixed $column_key [, mixed $index_key = null ] )

#2

Is there a built in way for me to simply extract each of these rows from the array without having to loop in.

是否有一个内置的方法可以让我简单地从数组中提取这些行，而不必循环。

Not yet. There will be a function soon named array_column(). However the complexity will be the same, it's just a bit more optimized because it's implemented in C and inside the PHP engine.

还没有。将会有一个名为array_column()的函数。但是复杂度是一样的，只是稍微优化了一点，因为它是在C语言中实现的，并且是在PHP引擎中实现的。

#3

Try this....

试试这个....

   foreach ($array as $val)
   {
       $thirdCol[] = $val[2];
   }

Youll endup with an array of all values from 3rd column

你将具有来自第三列的所有值的数组

#4

You could try this:

你可以试试这个:

$array["a"][0]=10;
$array["a"][1]=20;
$array["a"][2]=30;
$array["a"][3]=40;
$array["a"][4]=50;
$array["a"][5]=60;

$array["b"][0]="xx";
$array["b"][1]="yy";
$array["b"][2]="zz";
$array["b"][3]="aa";
$array["b"][4]="vv";
$array["b"][5]="rr";

$output = array_slice($array["b"], 0, count($array["b"]));

print_r($output);

#5

Another way to do the same would be something like $newArray = array_map( function($a) { return $a['desiredColumn']; }, $oldArray ); though I don't think it will make any significant (if any) improvement on the performance.

另一种方法是$newArray = array_map(函数($a)返回$a['desiredColumn']];},oldArray美元);虽然我不认为它会对性能有任何显著的改善。

#1