• kdb+

  abs() vs abs[] for fby “while” all() vs all[]

  Posted by kdb_newbie on May 18, 2024 at 12:17 pm

  May I ask how does abs() differs from abs[] in a select statement using fby clause?

  q)tab:([] sym:`g1`g3`g1`g1`g2`g3;price:-2.5 2 -0.5 -0.2 3 4)
  q)tab
  sym price
  ---------
  g1 -2.5
  g3 2
  g1 -0.5
  g1 -0.2
  g2 3
  g3 4
  
  q)select from tab where abs(price)=({abs max x};price) fby sym
  'type
  [0] select from tab where abs(price)=({abs max x};price) fby sym
  ^
  q)

  and also similarly, in my qsql, if I use all with square brackets, it throws a rank error but all() works fine

  select from xxx where all[col=`a;col2=`b] //rank error

  How do I know wher
  Thank you!

  rocuinneagain replied 6 months ago 2 Members · 1 Reply

  • all
  • fby
• 1 Reply

• 

  rocuinneagain

  Member

  May 20, 2024 at 8:45 am

  <div>See these sections of docs on:</div>

  • List Notation
  • Bracket Notation

  Order of evaluation also matters: Left-of-Right Evaluation

  abs(price)=({abs max x};price)
  

  Will run in order:

  1. ({abs max x};price)
  2. (price)=({abs max x};price)
     
  3. abs(price)=({abs max x};price)
     

  whereas:

  abs[price]=({abs max x};price)

  Will run in order:

  1. ({abs max x};price)
  2. abs[price]
  3. abs[price]=({abs max x};price)

  This tries to pass 2 arguments to all which only takes one argument so you get a rank error

  https://code.kx.com/q/ref/all-any/#all

  all[col=a;col2=b] 
  
  

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