/app/code/Magento/Backend/Block/Widget/Grid/Column/Filter/Range.php

<?php
/**
 * Magento
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade Magento to newer
 * versions in the future. If you wish to customize Magento for your
 * needs please refer to http://www.magentocommerce.com for more information.
 *
 * @category    Magento
 * @package     Magento_Backend
 * @copyright   Copyright (c) 2013 X.commerce, Inc. (http://www.magentocommerce.com)
 * @license     http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

/**
 * Range grid column filter
 *
 * @category   Magento
 * @package    Magento_Backend
 * @author      Magento Core Team <core@magentocommerce.com>
 */
namespace Magento\Backend\Block\Widget\Grid\Column\Filter;

class Range extends \Magento\Backend\Block\Widget\Grid\Column\Filter\AbstractFilter
{
    public function getHtml()
    {
        $html = '<div class="range"><div class="range-line">'
            . '<input type="text" name="' . $this->_getHtmlName()
            . '[from]" id="'.$this->_getHtmlId() . '_from" placeholder="'
            . __('From') . '" value="' . $this->getEscapedValue('from')
            . '" class="input-text no-changes" '
            . $this->getUiId('filter', $this->_getHtmlName(), 'from') . '/></div>';
        $html .= '<div class="range-line">'
            . '<input type="text" name="' . $this->_getHtmlName() . '[to]" id="'
            . $this->_getHtmlId() . '_to" placeholder="'
            . __('To') . '" value="' . $this->getEscapedValue('to') . '" class="input-text no-changes" '
            . $this->getUiId('filter', $this->_getHtmlName(), 'to') . '/></div></div>';
        return $html;
    }

    public function getValue($index=null)
    {
        if ($index) {
            return $this->getData('value', $index);
        }
        $value = $this->getData('value');
        if ((isset($value['from']) && strlen($value['from']) > 0)
            || (isset($value['to']) && strlen($value['to']) > 0)
        ) {
            return $value;
        }
        return null;
    }

    public function getCondition()
    {
        $value = $this->getValue();
        return $value;
    }
}