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<?php

add_action( 'genesis_loop', 'prefix_widget_area_helper' );
/**
 * Display a widgeted area with a grid loop post class.
 *
 * @since 1.0.0
 */
function prefix_widget_area_helper() {
	add_filter( 'post_class', 'prefix_grid_one_half' );
	genesis_widget_area( 'widget-area', array(
		'before' => '<div class="widget-area">',
		'after'  => '</div> <!-- end .widget-are -->',
	) );
	remove_filter( 'post_class', 'prefix_grid_one_half' );
}

<?php
/**
 * Simple Grid helper functions.
 *
 * @package     SimpleGrid
 * @subpackage  Genesis
 * @copyright   Copyright (c) 2014, Flagship, LLC
 * @license     GPL-2.0+
 * @since       1.0.0
 */

// Exit if accessed directly
if ( ! defined( 'ABSPATH' ) ) exit;

/**
 * Add post classes for a simple grid loop.
 *
 * @since      1.0.0
 * @category   Grid Loop
 * @param      $classes array An array of classes that should be appended
 * @param      $columns int   The number of grid items desired
 * @return     $classes array The grid classes
 */
function prefix_simple_grid( $classes, $columns ) {
	global $wp_query;

	//* Bail if we don't have a column number or it is invalid.
	if ( ! isset( $columns ) || ! in_array( $columns, array( 2, 3, 4, 6 ) ) ) {
		return;
	}

	$classes = array( 'simple-grid' );

	$column_classes = array(
		2 => 'one-half',
		3 => 'one-third',
		4 => 'one-fourth',
		6 => 'one-sixth'
	);

	$classes[] = $column_classes[absint($columns)];

	//* Add an "odd" class to allow for more control of grid collapse.
	if ( ( $wp_query->current_post + 1 ) % 2 ) {
		$classes[] = 'odd';
	}

	if( 0 === $wp_query->current_post || 0 === $wp_query->current_post % $columns ) {
		$classes[] = 'first';
	}

	return $classes;
}

/**
 * Set up a grid of one-half elements for use in a post_class filter.
 *
 * @since      1.0.0
 * @category   Grid Loop
 * @param      $classes array An array of the current post classes
 * @return     $classes array The post classes with the grid appended
 */
function prefix_grid_one_half( $classes ) {
	return array_merge( (array) prefix_simple_grid( $classes, 2 ), $classes );
}

/**
 * Set up a grid of one-third elements for use in a post_class filter.
 *
 * @since      1.0.0
 * @category   Grid Loop
 * @param      $classes array An array of the current post classes
 * @return     $classes array The post classes with the grid appended
 */
function prefix_grid_one_third( $classes ) {
	return array_merge( (array) prefix_simple_grid( $classes, 3 ), $classes );
}

/**
 * Set up a grid of one-fourth elements for use in a post_class filter.
 *
 * @since      1.0.0
 * @category   Grid Loop
 * @param      $classes array An array of the current post classes
 * @return     $classes array The post classes with the grid appended
 */
function prefix_grid_one_fourth( $classes ) {
	return array_merge( (array) prefix_simple_grid( $classes, 4 ), $classes );
}

/**
 * Set up a grid of one-sixth elements for use in a post_class filter.
 *
 * @since      1.0.0
 * @category   Grid Loop
 * @param      $classes array An array of the current post classes
 * @return     $classes array The post classes with the grid appended
 */
function prefix_grid_one_sixth( $classes ) {
	return array_merge( (array) prefix_simple_grid( $classes, 6 ), $classes );
}