sample.php

    /**
     * 配列の重複を削除
     *
     * @param [type] $arr
     * @param [type] $column
     * @return void
     */
    private function getUniqueArr($arr, $column)
    {
        $tmp = [];
        $uniqueArray = [];
        foreach ($arr as $value){
            if (!in_array($value[$column], $tmp)) {
                $tmp[] = $value[$column];
                $uniqueArray[] = $value;
            }
        }
        return $uniqueArray;
    }

sample.php

$project = $this->getUniqueArr($mergedArr, 'project_id');