How to use the fxjs.filter function in fxjs

return lefts.length && option.rels.length && go(option.rels, C.map(async function(me) {
                const query = me.query();
                if (query && query.text) query.text = query.text.replace(/^\s*WHERE/i, 'AND');

                var fold_key = me.rel_type == 'x' ?
                  `_#_${me.where_key.split('.')[1]}_#_` : me.where_key;

                const colums = uniq(add_column(me).originals.concat(
                  me.rel_type != 'x' ? me.as + '.' + me.where_key : me.where_key + ' AS ' + fold_key));

                const in_vals = filter(a => a != null, pluck(me.left_key, lefts));
                const is_row_num = me.row_number.length == 2;
                const rights = (!in_vals.length ? [] : await (is_row_num ?
                  QUERY `
                  SELECT *
                  FROM (
                    SELECT
                      ${COLUMN(...colums)}, 
                      ROW_NUMBER() OVER (PARTITION BY ${CL(me.where_key)} ORDER BY ${me.row_number[1]}) as "--row_number--"
                    FROM ${TB(me.table)} AS ${TB(me.as)} 
                    ${me.xjoin} 
                    WHERE ${IN(me.as +'.'+me.where_key, in_vals)} ${me.poly_type} ${tag(query)}
                  ) AS "--row_number_table--"
                  WHERE "--row_number_table--"."--row_number--"<=${me.row_number[0]}`
                  :
                  QUERY `
                  SELECT ${COLUMN(...colums)}

cmap(async function(me) {
              const f_key_ids = uniq(filter((r) => !!r, pluck(me.left_key, results)));
              if (me.rel_type == '-' || !f_key_ids.length) return recur([me, cat(map(r => r._ ? r._[me.as] : null, results))]);
              return go(
                (!me.left_join_over && me.left_joins.length ?
                  left_join_query : where_in_query)(me, SQL `WHERE ${IN(me.as + '.' + me.key, f_key_ids)}`, QUERY),
                group_by((v) => v[me.key]),
                function(groups) {
                  each(function(result) {
                    result._ = result._ || {};
                    result._[me.as] = (groups[result[me.left_key]] || []);
                  }, results);
                  return recur([me, cat(map(r => r._ ? r._[me.as] : null, results))]);
                }
              );
            }),
            () => results

return async function(strs, ...tails) {
      return go(
        ready_sqls(strs, tails),
        deep_flat,
        filter(t => t.as),
        each(option => {
          option.column = option.column || '*';
          option.query = option.query || tag();
          option.table = option.table || (option.rel_type == '-' ? plural(option.as) : option.as);
          option.rels = [];
          option.row_number = option.row_number || [];
        }),
        function setting([left, ...rest]) {
          const cur = [left];
          each(me => {
            while (!(last(cur).depth < me.depth)) cur.pop();
            const left = last(cur);
            left.rels.push(me);
            if (me.rel_type == '-') {
              me.left_key = me.left_key || (me.is_poly ? 'id' : singular(me.table) + '_id');
              me.where_key = me.key || (me.is_poly ? 'attached_id' : 'id');

return async function ljoin(strs, ...tails) {
      return go(
        ready_sqls(strs, tails),
        cat,
        filter(t => t.as),
        each(option => {
          option.query = option.query || tag();
          option.table = option.table || (option.rel_type == '-' ? option.as + 's' : option.as);
          option.column = option.column || CL(...table_columns[option.table]);
          option.left_joins = [];
          option.rels = [];
          option.row_number = option.row_number || [];
        }),
        ([left, ...rest]) => {
          const cur = [left];
          each(me => {
            while (!(last(cur).depth < me.depth)) cur.pop();
            const left = last(cur);
            if (me.rel_type == '-') {
              me.left_key = me.left_key || (me.is_poly ? 'id' : singular(me.table) + '_id');
              me.key = me.key || (me.is_poly ? 'attached_id' : 'id');