Simple German stemmer for Relevanssi

simple-german-stemmer.php

<?php
/*  Simple German stemmer

    A simple suffix stripper that can be used to stem German texts.
*/
add_filter( 'relevanssi_stemmer', 'relevanssi_simple_german_stemmer' );
function relevanssi_simple_german_stemmer(  $term  ) { 
	$term = str_replace( 'ß', 'ss', $term ); 
	$len = strlen( $term ); 
	$s_endings = array( 'b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 'r', 't' ); 
	$st_endings = array( 'b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 't' );

	$end3 = substr( $term, -3, 3 ); 
	$end2 = substr( $term, -2, 2 ); 
	$end1 = substr( $term, -1, 1 );

	if ( 'ern' === $end3 && $len > 5 ) { 
		$term = substr( $term, 0, -3 ); 
	} elseif ( 'em' === $end2 && $len > 5 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'er' === $end2 && $len > 5 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'en' === $end2 && $len > 5 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'es' === $end2 && $len > 5 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'e' === $end1 ) { 
		$term = substr( $term, 0, -1 );
	} elseif ( 's' === $end1 ) { 
		$second_to_last = substr( $term, -2, 1 ); 
		if ( in_array( $second_to_last, $s_endings ) ) $term = substr( $term, 0, -1 ); 
	} 
	$len = strlen( $term );

	$end3 = substr( $term, -3, 3 ); 
	$end2 = substr( $term, -2, 2 ); 
	if ( 'est' === $end3 && $len > 5 ) { 
		$term = substr( $term, 0, -3 ); 
	} elseif ( 'en' === $end2 && $len > 4 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'er' === $end2 && $len > 4 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'st' === $end2 ) { 
		$third_to_last = substr( $term, -3, 1 ); 
		if ( in_array( $third_to_last, $st_endings ) ) $term = substr( $term, 0, -2 ); 
	} 
	$len = strlen( $term ); 
	$end4 = substr( $term, -4, 4 ); 
	$end3 = substr( $term, -3, 3 ); 
	$end2 = substr( $term, -2, 2 ); 
	if ( 'isch' === $end4 && $len > 6 ) { 
		$term = substr( $term, 0, -4 ); 
	} elseif ( 'lich' === $end4 && $len > 6 ) { 
		$term = substr( $term, 0, -4 ); 
	} elseif ( 'heit' === $end4 && $len > 6 ) { 
		$term = substr( $term, 0, -4 ); 
	} elseif ( 'keit' === $end4 && $len > 6 ) { 
		$term = substr( $term, 0, -4 ); 
	} elseif ( 'end' === $end3 && $len > 5 ) { 
		$term = substr( $term, 0, -3 ); 
	} elseif ( 'ung' === $end3 && $len > 5 ) { 
		$term = substr( $term, 0, -3 ); 
	} elseif ( 'ik' === $end2 && $len > 4 ) { 
		$term = substr( $term, 0, -2 ); 
	} elseif ( 'ig' === $end2 && $len > 4 ) { 
		$term = substr( $term, 0, -2 ); 
	} 
	$term = str_replace( 'ä', 'a', $term ); 
	$term = str_replace( 'ö', 'o', $term ); 
	$term = str_replace( 'ü', 'u', $term );

	return $term; 
}

?>