New to KDB+, a entry question. Thanks for helping~

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1

Question1.
a: 1,2,3,4,5
b:1 2 3 4 5

c:(1;2;3;4;5)

What are the differences among them?

 

Question2.

What is

d:1;2;3;4;5

Question3.

aa:(4%0;-4%0;0;3)

bb:4%0, -4%0, 0, 3

What are the differences between them?

2

In general, Q executes right-to-left<o:p></o:p>

<o:p> </o:p>

And you can use ~ to compare data structures.<o:p></o:p>

<o:p> </o:p>

Q1: no difference<o:p></o:p>

q)a: 1,2,3,4,5<o:p></o:p>

q)b:1 2 3 4 5<o:p></o:p>

q)c:(1;2;3;4;5)<o:p></o:p>

q)a~b<o:p></o:p>

1b<o:p></o:p>

q)a~c<o:p></o:p>

1b<o:p></o:p>

<o:p> </o:p>

‘1.a’ takes the atom 5 and prepends 4 to it resulting in a 2-element list. Then prepends 3 to that to get a 3 element list. Ad naseum<o:p></o:p>

‘1.b’ is shorthand for creating a list – it only works for primitive non-mixed data types (like int lists below)<o:p></o:p>

‘1.c’ is the standard way to create a list and supports mixed data types – for example (1;`; “”)<o:p></o:p>

<o:p> </o:p>

Q2: ; is used to separate statements. So it assigns 1 to d then runs 2 then 3 then 4 then 5. And since the last statement doesn’t end in ; it prints the result (in this case 5)<o:p></o:p>

q)d:1;2;3;4;5<o:p></o:p>

5<o:p></o:p>

q)d<o:p></o:p>

1<o:p></o:p>

<o:p> </o:p>

<o:p> </o:p>

Q3:<o:p></o:p>

aa is creating a list with 4 elements as specified<o:p></o:p>

bb is creating a 4-element list but the elements are calculated in right-to left<o:p></o:p>

1)      0,0,3 creates a 3-element list<o:p></o:p>

2)      -4% divides -4 by each item in (1) ie: returns a list (-4%0;-4%0;-4%3) = -0w -0w -1.3333<o:p></o:p>

3)      0, prepends 0 to (2). Since it’s a different data type (0 is int/long vs (2) which is a float list) you get a mixed list<o:p></o:p>

4)      4% divides 4 by each (3) – ie: 0w -0 -0 -3  - since each element is now a float, it’s no longer a mixed list<o:p></o:p>

<o:p> </o:p>

<o:p> </o:p>

<o:p> </o:p>

From: personal-kdbplus@googlegroups.com [mailto:personal-kdbplus@googlegroups.com] On Behalf Of Yuxin Wei
Sent: Wednesday, August 5, 2015 8:10 AM
To: Kdb+ Personal Developers
Subject: [personal kdb+] New to KDB+, a entry question. Thanks for helping~<o:p></o:p>

<o:p> </o:p>

Question1.<o:p></o:p>

a: 1,2,3,4,5<o:p></o:p>

b:1 2 3 4 5<o:p></o:p>

c:(1;2;3;4;5)<o:p></o:p>

What are the differences among them?<o:p></o:p>

 <o:p></o:p>

Question2.<o:p></o:p>

What is<o:p></o:p>

d:1;2;3;4;5<o:p></o:p>

<o:p> </o:p>

Question3.<o:p></o:p>

aa:(4%0;-4%0;0;3)<o:p></o:p>

bb:4%0, -4%0, 0, 3<o:p></o:p>

What are the differences between them?<o:p></o:p>

<o:p> </o:p>

–
Submitted via Google Groups

3

Thank you sooooo much, and this answer really helps me out perfectly!

And I come up with some questions as well. I will post it during day time.

Thank you again and have a nice day!