将平面数组转换为按类别分组的数组

Question

我有一个如下所示的数据库表：

uid | group  | category
1   | group1 | cat1
2   | group1 | cat2
3   | group2 | cat3
4   | group2 | cat4
5   | group2 | cat5
6   | group3 | cat6
7   | group3 | cat7

但我需要将这些数据放在一个数组中，该数组按 group 对类别进行分组。

例如，我的数组应该是这样的：

Array
(
    [group1] => Array
        (
            [0] => Array
                (
                    [0] => 1
                    [1] => cat1

                )

            [1] => Array
                (
                    [0] => 2
                    [1] => cat2
                )

        )

    [group2] => Array
        (
            [0] => Array
                (
                    [0] => 3
                    [1] => cat3
                )

            [1] => Array
                (
                    [0] => 4
                    [1] => cat4
                )

            [2] => Array
                (
                    [0] => 5
                    [1] => cat5
                )

        )

    [group3] => Array
        (
            [0] => Array
                (
                    [0] => 6
                    [1] => cat6
                )
            [1] => Array
                (
                    [0] => 7
                    [1] => cat7
                )

        )

)

我已经写了一个 foreach 循环来做这个，但是我有一个问题。

我的问题是它总是遗漏表格的最后一行，我不知道如何解决它。在我看来，逻辑表明它应该始终有效。

我在想，在循环之后我可以将最后一行添加到新数组中，但我认为如果最后一行有不同的组，这可能会导致问题，我宁愿将解决方案内置到 foreach循环。

不幸的是，我在这里不知所措。如何修复我的代码以包含数据库查询的最后一行？

我也很想看看我可以对我当前的代码进行哪些改进，但这对于 codereview 来说可能是一个更好的问题。

我的循环：

$pass = [];
foreach($stmt as $key => $value) {
    if(empty($currentGroup)) $currentGroup = $value['group'];
    if(empty($temp)) $temp = [];
    if($currentGroup != $value['group'] || $key+1 == count($stmt)) {
        $pass[$currentGroup] = $temp;
        $currentGroup = $value['group'];
        $temp = [];
        $temp[] = [$stmt[$key]['uid'], $stmt[$key]['category']];
    } else {
        $temp[] = [$stmt[$key]['uid'], $stmt[$key]['category']];
    }
}

Answer 1

我最近又需要这个，所以我根据@JParkinson1991的回答做了一个函数。

我把它放在这里是为了记录，并可能帮助未来的读者。

function groupArray($arr, $group, $preserveSubArrays = false, $preserveGroupKey = false) {
    $temp = array();
    foreach($arr as $key => $value) {
        $groupValue = $value[$group];
        if(!$preserveGroupKey)
        {
            unset($arr[$key][$group]);
        }
        if(!array_key_exists($groupValue, $temp)) {
            $temp[$groupValue] = array();
        }

        if(!$preserveSubArrays){
            $data = count($arr[$key]) == 1? array_pop($arr[$key]) : $arr[$key];
        } else {
            $data = $arr[$key];
        }
        $temp[$groupValue][] = $data;
    }
    return $temp;
}

---

故障

function groupArray($arr, $group, $preserveGroupKey = false, $preserveSubArrays = false)

此函数接受 2 到 4 个参数。

1. 要分组的平面数组（数组）
2. 要分组的键（字符串/整数）
3. 在每个子数组的输出中保留组键的选项（布尔值）
4. 保留子数组的选项。如果每个子数组中仅存在 1 个键，则该函数将仅存储每行的单个值，而不是数组（布尔值）

第一个参数是数组本身，第二个参数是要分组的键，第三个（可选）参数是一个布尔值，告诉函数是否要在子数组中保留组键.

---

$temp = array();
foreach($arr as $key => $value) {
    $groupValue = $value[$group];
    if(!$preserveGroupKey)
    {
        unset($arr[$key][$group]);
    }
    if(!array_key_exists($groupValue, $temp)) {
        $temp[$groupValue] = array();
    }
    $temp[$groupValue][] = $arr[$key];
}

首先，我们创建一个名为$temp的临时数组

接下来，我们遍历数组，获取键（应该是字符串或 int）和值（应该是数组）。

我们将$groupValue 设置为您选择的$group 的任何值，例如下面示例中的“组”。

$arr = [
    0 => [
        "group" => "group1",
        "name" => "Bob",
    ],
    1 => [
        "group" => "group1",
        "name" => "Randy",
    ],
    2 => [
        "group" => "group1",
        "name" => "Susan",
    ],
    3 => [
        "group" => "group2",
        "name" => "Larry",
    ],
    4 => [
        "group" => "group2",
        "name" => "David",
    ],
    5 => [
        "group" => "group3",
        "name" => "Perry",
    ],
];

然后我们检查是否要$preserveGroupKey's。如果这个布尔值是假的（默认情况下），键将被删除，留下几个子数组，只剩下“名称”键。

现在我们检查$groupValue 是否存在于我们的$temp 数组中，如果不存在，我们就创建它。

然后我们将当前行的值添加到$temp[$groupValue]。从上面的例子中，我们最终会得到：

Array
(
    [group1] => Array
        (
            [0] => Bob
            [1] => Randy
            [2] => Susan
        )

    [group2] => Array
        (
            [0] => Larry
            [1] => David
        )

    [group3] => Array
        (
            [0] => Perry
        )

)

或者，将第三个参数设置为 true，您将得到：

Array
(
    [group1] => Array
        (
            [0] => Array
                (
                    [name] => Bob
                )

            [1] => Array
                (
                    [name] => Randy
                )

            [2] => Array
                (
                    [name] => Susan
                )

        )

    [group2] => Array
        (
            [0] => Array
                (
                    [name] => Larry
                )

            [1] => Array
                (
                    [name] => David
                )

        )

    [group3] => Array
        (
            [0] => Array
                (
                    [name] => Perry
                )

        )

)

Answer 2

以下应该这样做：

<?php

//Create an array to store our grouped rows
$grouped = array();

//Loop over all rows returned by the $stmt that has been executed.
//You could probably remove the key from here, it's not needed it seems.
//The keys within the $value array will match the names of the columns in 
//the database,
foreach($stmt as $key => $value){

    //As we're storing by the group value from the row we first want to
    //check if our grouped array contains a key for the group of the row
    //being processed. If it does not, create an empty array within the
    //grouped data for this group.
    if(!array_key_exists($value['group'], $grouped)){
        $grouped[$value['group']] = array();
    }

    //Knowing we will always have an array element for the rows group
    //we can blindly append the values for this row to the grouped 
    //container using its values.
    //'[] =' is just short hand append.
    $grouped[$value['group']][] = array(
        $value['uid'],
        $value['category']
    );
}

希望有帮助！

---

为了进一步证明这个循环，您可以将分组值追加更改为以下内容：

<?php

//Setting the whole row (minus the group) rather than just the uid 
//and category explicitly allows this code to work without modification
//as the datatable changes, ie. new columns. Assuming that is the 'group'
//column remains present
unset($value['group']);
$grouped[$value['group']][] = $value;

现在可以使用以下方式访问分组内容数据：

<?php

//Acceess data via column name not array index, yay!
echo $grouped['group1']['uid']