Similar posts by category in WordPress which excludes the current post

wp_similar_posts_by_category.php

<?php
/**
 * Similar posts loop
 */
$categories = get_the_category(); //get all categories for this post
$cat_id = $categories[0]->cat_ID;
echo $cat_id;
$args = array(
	'orderby' 			=> 'date',
	'order' 			=> 'DESC',
	'post_type' 		=> 'post',
	'posts_per_page' 	=> 2,
	'post__not_in' 		=> array($post->ID),
	'category__in' 		=> $cat_id,
); // post__not_in will exclude the current post

$wt_query = new WP_Query( $args );

if($wt_query->have_posts()) :
	while ($wt_query->have_posts()) :
		$wt_query->the_post();
		the_title();
	endwhile;
	wp_reset_postdata();
else :
  echo '<p>'.<?php _e( 'Sorry, no posts matched your criteria.' ); ?>.'</p>'
endif;
?>