The writing rules for expression x in loop functions

Description:

Introduce the common rules on expressions in loop functions.

Note:

Expression x in loop functions such as r.(x), r.run(x), A.(x), A.run(x) and so on, should follow the rules below:

 

1. Members: ~ and A.~. ~ means the record being processed currently.

	A
1	=demo.query("select * from EMPLOYEE")
2	=A1.(age(~.HIREDATE))	[9,6,3,7,9,8,…]
3	=A1.new(~.NAME:Name,age(~.HIREDATE):Workage)

 

2. Ordinal numbers: # and A.#. # indicates the ordinal number of the members.

	A	[1,2,3,4,5,6,7,8…], the two results are the same.
1	=demo.query("select * from EMPLOYEE")
2	=A1.(#)
3	=A1.(A1.#)

 

3. Fields: F, ~.F, r.F and A. F are equal to A.~. F , and A.F is equal to A(1).F if there is not a loop.

	A
1	=demo.query("select * from EMPLOYEE")
2	=A1.(age(HIREDATE))
3	=A1.(age(~.HIREDATE))	Same result as A2.
4	=A1.(age(A1.HIREDATE))	Same result as A2.
5	=A1.HIREDATE	2005-03-11, it is equal to A1(1).HIREDATE if there is not a loop.

 

4. A[i] and ~[i] are equal to A(#+i) in the loop, which counts the members forward from the current member in A.

 

5. Return the i^th member and if the boundary is exceeded, errors are not reported and null is returned. F[…] is equal to A[…].F.

	A
1	=demo.query("select ORDERID,AMOUNT,'' as ACCUMULATION from SALES")
2	=A1.run(ACCUMULATION=AMOUNT+ACCUMULATION[-1])	Obtain the current ACCUMULATION by adding the ACCUMULATION of the last record to the current AMOUNT.

 

6. A[a:b] and ~[a:b] in the loop indicate a sequence composed of members between A(#+a) and A(#+b).

 

7. Return a sequence consisting of members within the specified interval. a is 1-# by default and b is A.len()-# by default.

	A
1	=demo.query("select STOCKID,DATE,CLOSING,'' as FirstThree from STOCKRECORDS")
2	=A1.run(FIRSTTHREE=~[--3:-1].(CLOSING).avg())	~[-3:-1] indicates a sequence composed of three records counted backward from the current row.

 

8. Iteration: A1.f1(A2.f2(x))

 

Symbols in expression x will be first identified to serve A2; if expression x serves A1, the iteration will be _. A1.f1(A2.f2(A1.x)).

	A
1	=demo.query("select * from EMPLOYEE")
2	=demo.query("select * from DEPARTMENT")
3	=A2.run(MANAGER=A1.select@1(EID==A2.~.MANAGER).NAME)	Reference the nested loop.

 

9. Aggregate: A.f(x) 

A.f(x) is equal to A.(x).f(), in which f is an aggregate function and x can be null.

 

Note: The x in A.count(x) is a Boolean expression, which is different from the rule for other aggregate functions.

 

10. get(level,F;a:b)

Get information of base members at a superior level in a multilayer loop function

	A
1	[1,2,3]
2	=A1.(A1.(abs(~-get(1))))	Calculate the maximum distance from each value to the others.
3	=demo.query("select * from employee")
4	=A3.derive(A3.max(abs(SALARY-get(1,SALARY))):MaxDiff)	Calculate the maximum salary difference for each employee compared with every other employee.