cw_editdistance.sqlx

config { hasOutput: true }
/*
 * Copyright 2022 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* Similar to teradata's editdistance without weightages */
CREATE OR REPLACE FUNCTION ${self()}( a STRING, b STRING ) RETURNS INT64
LANGUAGE js 
OPTIONS (
    description="Similar to teradata's editdistance without weightages"
)
AS """

    if ( a == null || b == null ) {
        return null;
    }

    var work = new Array( a.length + 1 )
    for ( var i = 0 ; i <= a.length ; i ++ ) {
        work[i] = new Array ( b.length + 1 )
    }


    for ( var i = 0 ; i < a.length + 1 ; i ++ )
        work[i][0] = i;

    for ( var j = 0 ; j < b.length + 1 ; j ++ )
        work[0][j] = j;


    for ( var i = 1 ; i < a.length + 1 ; i ++ ) {
        for ( var j = 1 ; j < b.length + 1 ; j ++ ) {
            var cost = a[i-1] == b[j-1] ? 0 : 1;
            work[i][j] = Math.min(
                work[i-1] [j]   + 1,
                work[i]   [j-1] + 1,
                work[i-1] [j-1] + cost )
            if ( i > 1 && j > 1 && a[i-1] == b[j-2] && a[i-2] == b[j-1] ) {
                work[i][j] = Math.min(
                    work[i]  [j],
                    work[i-2][j-2] + 1 );
            }
        }
    }
    return work[a.length][b.length];
""";