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:
Ø Members: ~ and A.~. ~ means the record being processed currently.
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A |
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=demo.query("select * from EMPLOYEE") |
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=A1.(age(~.HIREDATE)) |
[9,6,3,7,9,8,…] |
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=A1.new(~.NAME:Name,age(~.HIREDATE):Workage) |
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Ø Ordinal numbers: # and A.#. # indicates the ordinal number of the members.
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A |
[1,2,3,4,5,6,7,8…], the two results are the same |
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=demo.query("select * from EMPLOYEE") |
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2 |
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=A1.(A1.#) |
Ø 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.
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A |
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=demo.query("select * from EMPLOYEE") |
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2 |
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[9,6,3,7,9,8,…], the results of the three expressions are the same.
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3 |
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=A1.(age(A1.HIREDATE)) |
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=A1.HIREDATE |
2005-03-11, it is equal to A1(1).HIREDATE if there is not a loop. |
Ø A[i] and ~[i] are equal to A(#+i) in the loop, which counts the members forward from the current member in A and return the ith member. If the boundary is exceeded, errors are not reported and null is returned. F[…] is equal to A[…].F
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A |
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=demo.query("select ORDERID,AMOUNT,'' as ACCUMULATION from SALES") |
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=A1.run(ACCUMULATION=AMOUNT+ACCUMULATION[-1]) |
Obtain the current ACCUMULATION by adding the ACCUMULATION of the last record to the current AMOUNT. |
Ø A[a,b] and ~[a,b] in the loop indicate a sequence composed of members between A(#+a) and A(#+b). a is 1-# by default and b is A.len()-# by default.
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A |
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=demo.query("select STOCKID,DATE,CLOSING,'' as FirstThree from STOCKRECORDS") |
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=A1.run(FIRSTTHREE=~[--3,-1].(CLOSING).avg()) |
~[-3,-1] indicates a sequence composed of three records counted backward from the current row. |
Ø 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)).
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A |
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=demo.query("select * from EMPLOYEE") |
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=demo.query("select * from DEPARTMENT") |
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=A2.run(MANAGER=A1.select@1(EID==A2.~.MANAGER).NAME) |
Reference the nested loop |
Ø 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.
Ø get(level,F;a:b)
Get information of base members at a superior level in a multilayer loop function
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A |
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[1,2,3] |
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=A1.(A1.(abs(~-get(1)))) |
Calculate the maximum distance from each value to the others |
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=demo.query("select * from employee") |
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=A3.derive(A3.max(abs(SALARY-get(1,SALARY))):MaxDiff) |
Calculate the maximum salary difference for each employee compared with every other employee |