Matrikx reloaded
(all work and no k makes jack a dull boy)
Although the array language K is immediately accessible to programmers familiar with APL or J, comparatively few have spent any time looking into it. For anyone who wants to add a new language to their toolkit this short article describes how to download and install a trial version – and points to further information for those who would like to learn more.
Installation:
Download and run a copy of kdbsetup.exe from the download page [2] of the Kx website [1], this 200K file will install the array language K and the database Kdb. It will install on any dialect of Windows, although NT or XP are more comfortable to use as the 95/98/ME command prompt is so clunky.
The trial version has restrictions on the amount of data it will work with, and the number of messages that can be sent between K sessions – but otherwise is a full version.
Try K:
Open a command window, and type
k
and you’ll be in immediate execution mode in a K session, try a few familiar things:
C:\k>k K 2.95t 2003-04-03 Copyright (C) 1993-2003 Kx Systems Evaluation. Not for commercial use. \ for help. \\ to exit. 2+2 4 2+2 3 4 4 5 6 +/2 3 4 9
to get out just type \\ in immediate execution mode.
K includes a built in reference, access it by typing a single \ followed by a return in immediate execution, that will give you a list of pages available. Enter the particular one you want to see (\+ to list the verbs for example).
If you type something complicated and get suspended you can clear the execution stack with a single \ at the suspension prompt. Here a nonsense function foo is defined to add its argument to a string and cause an error:
foo:{"string"+x}
foo 17
type error
{"string"+x}
^
> \
If you just want to disable suspensions while looking around enter the command \e 0 on a new line – the error will still be displayed but the stack will be cut back:
\e 0 foo 17 type error Try Kdb:
Get out of your previous K session if you still have it open by entering \\ and then start a Kdb session by entering:
k db this time you’ll be in a kdb session as shown by the ksql> prompt: C:\k>k db K 2.95t 2003-04-03 Copyright (C) 1993-2003 Kx Systems Evaluation. Not for commercial use. \ for help. \\ to exit. KDB 2.5t 2003-06-25 ksql>
as Kdb is a database we’ll load in a sample database to make things more interesting, at the ksql> prompt type in:
ksql>load 'trade.t'
ksql>
Note the single quotes, strings are delimited by double quotes in K, single quotes in Kdb – that makes it easier to embed KSQL strings in K code.
Now try some simple KSQL:
ksql>tables
`stock `trade
ksql>vars stock
`stock `industry
ksql>count stock
6
ksql>select from stock where industry='auto'
.((`stock
`xx `yyyy
.,(`K;1;))
(`industry
`auto `auto
))
ksql>count trade
100000
ksql>vars trade
`stock `price `amount `date
ksql>select avg price by stock from trade
.((`stock
`aaa `bbb `ccc `dd `xx `yyyy
.((`T
,`stock
)
(`K;1;)))
(`price
74.93937 74.93437 74.89528 74.95792 74.73562 74.71044
))
ksql>
Notice that the table columns are just vectors: At last – a database that you can work with not against/despite! You can open a simple viewer on the database by typing in:
ksql>show ''
or you can view the results of a query by prefixing a show to the constraint:
ksql>show select avg price by stock from trade
you can escape from Kdb to K by entering a single \ at the ksql> prompt
ksql>\ 2+2 3 4 4 5 6
and you return from K to Kdb by entering .d.l`
ksql>\ count stock value error count ^ parse error .d.l` ksql>count stock 6 ksql>
exit from a Kdb session with \\ as you would from a K session.
Summaries of KSQL, and the Kdb SQL92 implementation can be found in the two files s.txt (SQL92) and t.txt (KSQL) in the directory c:\k\db created when you installed kdb earlier.
Documentation:
If the 5-10 minutes it took to try this out has caught your interest the best way to learn the basics of K and Kdb is to read through the Kdb manual Getting started with Kdb available from the Documentation page [3] on the Kx website. Although its focus is on Kdb it takes you through the basics of K as well.
Apart from the other manuals on the Documentation page [3] there is a K reference card available from Mike Powell’s directory on the User Contributions page [4].
When learning a new language it’s often helpful to have other people’s code to read, there is a large library of K and Kdb code on the Kx site in Arthur Whitney’s directories [7].
More general articles about K and Kdb are indexed on Eberhard Lutz’s Kaylang page [8]
More Information and Help:
If you have questions about K or Kdb the Kxforums [5] are open to anyone, or the K and Kdb listboxes can be searched from the archive page [6]
Links:
[1] http://kx.com – home of k and kdb
[2] http://www.kx.com/download/download.htm – download k and kdb
[3] http://www.kx.com/download/documentation.htm – manuals
[4] http://www.kx.com/download/contributors.htm – user contributions
[5] http://kxforums.com/kxf/ – user forums
[6] http://www.kx.com/listbox/index.html – k and kdb listbox archives
[7] http://kx.com/a/ – sample code
[8] http://www.e7l3.com/kaylang.html – extensive list of k articles