bmoredrew/sort-by-acf-repeater-field.php

## sort-by-acf-repeater-field.php
<?php

  // Create an empty array for storage
  $post_data = array();

  // Set arguments for your query
  $args = array(
      'post_type'         => 'trips',
      'posts_per_page'    => 999
  );

  // Do our query with any arguments from above
  $query = new WP_Query( $args );
  if ( $query->have_posts() )
  {
      while ( $query->have_posts() )
      {
          $query->the_post();
          // Setup our repeater
          if( have_rows('trip_info') ):
              while ( have_rows('trip_info') ) : the_row();
                  // Optional - Only get posts that match a true false within our repeater
                  if ( get_sub_field('featured_trip') )
                  {
                      // Build our array with the data we need using key => value
                      $post_data[] = array(
                          'title' => get_the_title(),
                          'date'  => get_sub_field('trip_date')
                      );
                  }
              endwhile;
          endif;
      }
  }

  // Custom function to use in our sort to list the items by date
  function subval_sort( $a, $b )
  {
      if ( $a['date'] == $b['date'] )
          return 0;
      return $a['date'] < $b['date'] ? -1 : 1;
  }

  // Sort our multidimensional array by sub array value
  usort( $post_data, 'subval_sort' );

  // We can now work our data normally through easy to access methods
  foreach ( $post_data as $post )
  {
      echo $post['title'] . '&nbsp; ' ;
      echo $post['date'];
      echo '<br/>';
  }
	<?php

	// Create an empty array for storage
	$post_data = array();

	// Set arguments for your query
	$args = array(
	'post_type' => 'trips',
	'posts_per_page' => 999
	);

	// Do our query with any arguments from above
	$query = new WP_Query( $args );
	if ( $query->have_posts() )
	{
	while ( $query->have_posts() )
	{
	$query->the_post();
	// Setup our repeater
	if( have_rows('trip_info') ):
	while ( have_rows('trip_info') ) : the_row();
	// Optional - Only get posts that match a true false within our repeater
	if ( get_sub_field('featured_trip') )
	{
	// Build our array with the data we need using key => value
	$post_data[] = array(
	'title' => get_the_title(),
	'date' => get_sub_field('trip_date')
	);
	}
	endwhile;
	endif;
	}
	}

	// Custom function to use in our sort to list the items by date
	function subval_sort( $a, $b )
	{
	if ( $a['date'] == $b['date'] )
	return 0;
	return $a['date'] < $b['date'] ? -1 : 1;
	}

	// Sort our multidimensional array by sub array value
	usort( $post_data, 'subval_sort' );

	// We can now work our data normally through easy to access methods
	foreach ( $post_data as $post )
	{
	echo $post['title'] . '  ' ;
	echo $post['date'];
	echo '<br/>';
	}