kdb/q update a keyed table element's list element

Question

I have a table like:

q)tbl[`XXX]
1977 1987 1997

and I want to update the nth element from the list of years, so the above becomes

q)tbl[`XXX]
1997 1987 2007

And need it to be inplace? Been looking into the docs but having hard figuring it out.

Answer 1

You can think of the table as a flipped dictionary. To do a dictionary update, you index in on key first:

  q)tbl:([]XXX:1977 1987 1997)
  q)dict:flip tbl
  q)dict[`XXX;n]:2007
  q)dict
  XXX| 1977 1987 2007

Therefore to do an inplace update on a table the following syntax is used:

  q)tbl:([]XXX:1977 1987 1997)
  q)tbl[`XXX]
  1977 1987 1997
  q)tbl[n;`XXX]:2007
  q)tbl[`XXX]
  1977 1987 2007