apply substring function to each entry in kdb query

[Sam]

How do I apply substring function for each entry in a query in KDB/Q?

> s:"hello"
> s[0 1]
> "he"

> # apply this to string column 'col' in following query
> select col from tab

[Mohammad Noor]

If you have a string column, you have a nested list - to index into nested lists see http://code.kx.com/wiki/JB:QforMortals2/lists#Elided_Indices

Example:

q)show tab:([] col:(0N 5)#15?.Q.a)
  col
  -------
  "mikbj"
  "lfuwg"
  "byfen"
q)select col[;0 1] from tab
  x
  ----
  "mi"
  "lf"
  "by"

Note, if you only want the first N chars (or last -N chars) can use # (take) with adverb:

q)select 2#'col from tab
  col
  ----
  "mi"
  "lf"
  "by"

Mohammad Noor

[Samit Jain]

Wonderful.  Thanks :)

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[Sean O'Hagan]

Don't forget about sublist...http://code.kx.com/wiki/Reference/sublist

select 2 sublist'col from tab

Cheers,

Sean