How to group subarrays by a column value?

Question

I have the following array

Array
(
    [0] => Array
        (
            [id] => 96
            [shipping_no] => 212755-1
            [part_no] =&         


        

Answer 1

1. GROUP BY one key

This function works as GROUP BY for array, but with one important limitation: Only one grouping "column" ($identifier) is possible.

function arrayUniqueByIdentifier(array $array, string $identifier)
{
    $ids = array_column($array, $identifier);
    $ids = array_unique($ids);
    $array = array_filter($array,
        function ($key, $value) use($ids) {
            return in_array($value, array_keys($ids));
        }, ARRAY_FILTER_USE_BOTH);
    return $array;
}

---

2. Detecting the unique rows for a table (twodimensional array)

This function is for filtering "rows". If we say, a twodimensional array is a table, then its each element is a row. So, we can remove the duplicated rows with this function. Two rows (elements of the first dimension) are equal, if all their columns (elements of the second dimension) are equal. To the comparsion of "column" values applies: If a value is of a simple type, the value itself will be use on comparing; otherwise its type (array, object, resource, unknown type) will be used.

The strategy is simple: Make from the original array a shallow array, where the elements are imploded "columns" of the original array; then apply array_unique(...) on it; and as last use the detected IDs for filtering of the original array.

function arrayUniqueByRow(array $table = [], string $implodeSeparator)
{
    $elementStrings = [];
    foreach ($table as $row) {
        // To avoid notices like "Array to string conversion".
        $elementPreparedForImplode = array_map(
            function ($field) {
                $valueType = gettype($field);
                $simpleTypes = ['boolean', 'integer', 'double', 'float', 'string', 'NULL'];
                $field = in_array($valueType, $simpleTypes) ? $field : $valueType;
                return $field;
            }, $row
        );
        $elementStrings[] = implode($implodeSeparator, $elementPreparedForImplode);
    }
    $elementStringsUnique = array_unique($elementStrings);
    $table = array_intersect_key($table, $elementStringsUnique);
    return $table;
}

It's also possible to improve the comparing, detecting the "column" value's class, if its type is object.

The $implodeSeparator should be more or less complex, z.B. spl_object_hash($this).

---

3. Detecting the rows with unique identifier columns for a table (twodimensional array)

This solution relies on the 2nd one. Now the complete "row" doesn't need to be unique. Two "rows" (elements of the first dimension) are equal now, if all relevant "fields" (elements of the second dimension) of the one "row" are equal to the according "fields" (elements with the same key).

The "relevant" "fields" are the "fields" (elements of the second dimension), which have key, that equals to one of the elements of the passed "identifiers".

function arrayUniqueByMultipleIdentifiers(array $table, array $identifiers, string $implodeSeparator = null)
{
    $arrayForMakingUniqueByRow = $removeArrayColumns($table, $identifiers, true);
    $arrayUniqueByRow = $arrayUniqueByRow($arrayForMakingUniqueByRow, $implodeSeparator);
    $arrayUniqueByMultipleIdentifiers = array_intersect_key($table, $arrayUniqueByRow);
    return $arrayUniqueByMultipleIdentifiers;
}

function removeArrayColumns(array $table, array $columnNames, bool $isWhitelist = false)
{
    foreach ($table as $rowKey => $row) {
        if (is_array($row)) {
            if ($isWhitelist) {
                foreach ($row as $fieldName => $fieldValue) {
                    if (!in_array($fieldName, $columnNames)) {
                        unset($table[$rowKey][$fieldName]);
                    }
                }
            } else {
                foreach ($row as $fieldName => $fieldValue) {
                    if (in_array($fieldName, $columnNames)) {
                        unset($table[$rowKey][$fieldName]);
                    }
                }
            }
        }
    }
    return $table;
}