May 19, 2011

How can I reorder column names of a splayed table on disk?

Modify the file .d in the splayed table directory. The contents are editable via operators get and set.

    $ rlwrap q sp.q
    KDB+ 2.7 2011.02.16 Copyright © 1993-2011 Kx Systems
    +`p`city!(`p$`p1`p2`p3`p4`p5`p6`p1`p2;`london`london`london..
    (+(,`color)!,`blue`green`red)!+(,`qty)!,900 1000 1200
    +`s`p`qty!(`s$`s1`s1`s1`s2`s3`s4;`p$`p1`p4`p6`p2`p2`p4;300 ..
    q)sp
    s p qty
    ———
    s1 p1 300
    s1 p2 200
    s1 p3 400
    q)`:splaydir/ set sp
    `:splaydir/
    q)\ls -a splaydir
    ,”.”
    “..”
    “.d” // this is where the col names live
    ,”p”
    “qty”
    ,”s”
    q)get `:splaydir/.d
    `s`p`qty
    q)`:splaydir/.d set reverse get `:splaydir/.d
    `:splaydir/.d
    q)get `:splaydir/.d
    `qty`p`s
    q)

Verify with a fresh kdb instance:

$ rlwrap q splaydir
KDB+ 2.7 2011.02.16 Copyright © 1993-2011 Kx Systems
q)\v
,`splaydir
q)splaydir
qty p s
——-
300 0 0
200 1 0
400 2 0
q)

See also: xcol and xcols faq{.}

See Also