Code snippets for the Yoast SEO canonical output

yoast_seo_canonical_change_woocom_shop.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Change the canonical link for the shop page
 * Credit: Scott Weiss of somethumb.com
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Jan 25 2017 using Yoast SEO 6.0 on WordPress 4.9.1
 */

add_filter( 'wpseo_canonical', 'yoast_seo_canonical_change_woocom_shop', 10, 1 );

function yoast_seo_canonical_change_woocom_shop( $canonical ) {
	if ( !is_shop() ) {
		return $canonical;
	}
    return get_permalink( woocommerce_get_page_id( 'shop' ) );
}

yoast_seo_canonical_remove.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Remove Yoast SEO Canonical From All Pages
 * Credit: Yoast Team
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Jun 16 2017 using Yoast SEO 4.9 on WordPress 4.8
 */

add_filter( 'wpseo_canonical', '__return_false' );

yoast_seo_canonical_remove_post.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Remove Yoast SEO Canonical From Individual or Multiple Items
 * Credit: Yoast Team
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Jun 16 2017 using Yoast SEO 4.9 on WordPress 4.8
 *********
 * DIFFERENT POST TYPES
 * Post: Change 123456 to the post ID
 * Page: Change is_single to is_page and 123456 to the page ID
 * Custom Post Type: Change is_single to is_singular and 123456 to the 'post_type_slug'
    Example: is_singular( 'cpt_slug' )
 *********
 * MULTIPLE ITEMS
 * Multiple of the same type can use an array.
    Example: is_single( array( 123456, 1234567, 12345678 ) )
 * Multiple of different types can repeat the if statement
 */
 
add_filter( 'wpseo_canonical', 'yoast_remove_canonical_items' );

function yoast_remove_canonical_items( $canonical ) {
  if ( is_single ( 123456 ) ) {
    return false;
  }
  /* Use a second if statement here when needed */
	return $canonical; /* Do not remove this line */
}

yoast_seo_canonical_remove_search.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Remove Yoast SEO Canonical From Search Pages Only
 * Credit: Yoast Team
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Jun 16 2017 using Yoast SEO 4.9 on WordPress 4.8
 */

add_filter( 'wpseo_canonical', 'yoast_remove_canonical_search' );

function yoast_remove_canonical_search( $canonical ) {
	if( is_search() ) {
		return false;
	} else {
		return $canonical;
	}
}

yoast_seo_canonical_slash_add.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Add trailing slash to all Yoast SEO canonicals
 * Credit: Unknown
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Oct 25 2019 using Yoast SEO 12.3 on WordPress 5.2.4
 */
 
add_filter( 'wpseo_canonical', 'yoast_seo_canonical_slash_add' );

function yoast_seo_canonical_slash_add( $canonical_url ) {
         return trailingslashit( $canonical_url );
}

yoast_seo_canonical_slash_remove.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Remove trailing slash from all Yoast SEO canonicals
 * Credit: Unknown
 * Yoast Doc: https://developer.yoast.com/features/seo-tags/canonical-urls/api/
 * Last Tested: Oct 25 2019 using Yoast SEO 12.3 on WordPress 5.2.4
 */
 
add_filter( 'wpseo_canonical', 'yoast_seo_canonical_slash_remove' );

function yoast_seo_canonical_slash_remove( $canonical_url ) {
         return untrailingslashit( $canonical_url );
}

If you want to remove canonical tag from the requests with url parameters. You can use this.

function custom_remove_canonical_with_get_params( $canonical ) {
    // Check if there are any GET parameters in the URL
    if ( ! empty( $_GET ) ) {
        // If there are GET parameters, return the current URL without any canonical tag
        return false;
    }

    // If there are no GET parameters, return the original canonical URL
    return $canonical;
}
add_filter( 'wpseo_canonical', 'custom_remove_canonical_with_get_params' );