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  Why does this work: value each {x+y+z}[1;;],’enlist (2;enlist 3)

  Posted by mannix on April 14, 2022 at 12:00 am

  I understand the function and the projec`tion.

  I’m wondering what is ”   ,’    ” and why is it used here

  Why do we enlist the list, and enlist 3 inside the list but not 2.

  What is the “each” doing here, as far as I can see {x+y+z}[1;;],’enlist (2;enlist 3) is one thing in itself?

  mannix replied 8 months, 2 weeks ago 2 Members · 1 Reply
• 1 Reply

• 

  eohara

  Member

  April 14, 2022 at 12:00 am

  Might be best to deal with this in pieces

  q)(2;3)
  2 3
  q)(2;enlist 3)
  2
  ,3

  Here, the enlist is to prevent 2 and 3 concatenating into a simple list of longs.

  The difference in the final output is an extra level of enlisting:

  q)value each{x+y+z}[1;;],’enlist(2;3)
  ,6
  q)value each{x+y+z}[1;;],’enlist(2;enlist 3)
  6
  q)type value each{x+y+z}[1;;],’enlist(2;enlist 3)
  0h
  q)type value each{x+y+z}[1;;],’enlist(2;3)
  7h

  Why the other enlist?

  q){x+y+z}[1;;],'(2;enlist 3)
  {x+y+z}[1;;] 2
  {x+y+z}[1;;] 3
  q){x+y+z}[1;;],’enlist(2;enlist 3)
  {x+y+z}[1;;] 2 ,3

  In the first example, each element of the right-hand list (2 and ,3) is joined to the projection, which results in two projections being returned.
  With the enlist, the right-hand side is now a one-element list (the element being (2;,3)). This is joined to the projection.

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