filter：过滤数据，只有符合特定条件的数据才会被保留下来，然后进入下一个数据流。
1）等值比较
filter data by $0 == 1
filter data by $0 != 1
2）字符串 正则匹配 JAVA的正则表达式
字符串以CM开头
filter data by $0 matches 'CM.*';
字符串包含CM
filter data by $0 matches '.*CM.*';
3）not
filter data by not $0==1;
filter data by not $0 matches '.*CM.*';
4）NULL处理
filter data by $0 is not null;
5）UDF
filter data by isValidate($0);
6）and or
filter data by $0!=1 and $1>10