Here’s how to use pselect() function.
Description:
Get positions of the specified members from a sequence.
Syntax:
|
A.pselect(x,k) |
Search from the kth member when parameter k is present |
|
A.pselect(x1:y1,x2:y2,......xi:yi) |
The simplified syntax for the composite query using "&&" . It is equal to A.pselect(x1==y1 && x2==y2 &&...... xi==yi) |
Note:
The function gets the position of a member in sequence A and returns the sequence number of a member that fulfils condition x, or returns an empty sequence/null if it cannot find the eligible member. The return value is also subject to the option working with the function.
Option:
|
@a |
Return a sequence composed of sequence numbers of all the members that fulfill the condition x; when it is not supplied, return the sequence number of the first eligible member |
|
@z |
Perform the search backwards from the last member; by default, perform the search from the first member |
|
@b |
Perform the binary search when A is by default a sequence in ascending order. Note that in this case xi must be in ascending order; if A is not an ascendingly ordered sequence, this option could return incorrect result; when it is used with A.pselect(x1:y1,x2:y2,......xi:yi) to find out members that make cmp(x,y) return 0, simply write A.pselect@b(x1:y1,x2:y2,......xi:yi) without including cmp() |
|
@s |
It requires that members in A are ascendingly ordered for expression x; with the binary search, if no members in A can make the expression x return 0, then return the opposite number of the position where x can be inserted |
|
@n |
If no sequence member is found, return the result of the length of A plus 1; this option and @a are mutually exclusive |
|
@0 |
Return 0 when the eligible member isn’t found; this option and @n option are mutually-exclusive |
Parameter:
|
A |
A sequence |
|
x |
A Boolean expression, whose value can be null. When using @b option, x should be an expression whose return value is an integer |
|
k |
Search from the kth member |
|
xi:yi |
xi is an expression, and yi is a comparing value |
Return value:
The sequence numbers of the member that fulfils condition x or that makes the result of expression x equals y in the given sequence. @a option works to return a sequence composed of all the sequence numbers of the member that fulfils condition x, and return a sequence composed of the sequence numbers of all the members when x is null.
Example:
|
|
A |
|
|
1 |
[2,5,4,3,2,9,4,9,3] |
|
|
2 |
=A1.pselect(~>4) |
2 |
|
3 |
=A1.pselect@a(~>4) |
[2,6,8] |
|
4 |
=A1.pselect@z(~>4) |
8 |
|
5 |
=A1.pselect@az(~>4) |
[8,6,2] |
|
6 |
=[1,3,5,7,9].pselect@b(~-5) |
3; here the syntax is equal to A7’s, and both A6 and A7 return the same result. |
|
7 |
=[1,3,5,7,9].pselect@b(~:5) |
When colon is used, @b won’t change the syntax. |
|
8 |
=[1,3,5,7,9].pselect@s(~:4) |
-3; cannot find 4 and return the opposite number of the position where 4 can be inserted. |
|
9 |
=[1,3,5,7,9].pselect@n(~:4) |
6 |
|
10 |
=demo.query("select * from EMPLOYEE") |
|
|
11 |
=A10.pselect(GENDER:"M",DEPT:"Sales") |
6 |
|
12 |
=demo.query("select * from EMPLOYEE where GENDER='M' order by EID asc") |
EID and GENDER are in the same order. |
|
13 |
=A12.pselect@b(EID:10,GENDER:"M") |
2 |
|
14 |
=A12.pselect@s(EID:3,GENDER:"M") |
-1; cannot find the record satisfying EID=3 and GENDER=M and return the opposite number of the position where the record can be inserted. |
|
15 |
=A12.pselect@n(EID:3,GENDER:"M") |
239 |
|
16 |
=[2,5,4,3,2,9,4,9,3].pselect(~>4,3) |
6 |
|
17 |
=[2,5,4,3,2,9,4,9,3].pselect@0(~>9) |
0 |
Note:
A must be an ascendingly ordered sequence and xi in ascending order when @b or @s is used, otherwise they will bring about incorrect results.