Frequently-asked questions from the k4 listbox¶
If you notice a question that is asked more then once on the k4 list, please feel free to add it here.
Where can I find archives of the k4 list?¶
Archives are available to subscribers at the Topicbox. When you follow that link, you will be asked for your e-mail address and the mailing list name. Use k4 for the list name, and the e-mail address that you used to subscribe to the k4 list.
How to post test data on the k4 list?¶
Always post your test data in the executable form. For example,
q)foo:([]a:5?10;b:5?10;c:5?10)You can generate an executable form of your data using 0N!.
q)0N!foo;
+`a`b`c!(4 3 7 1 1;6 1 7 9 8;4 7 5 0 9)Note use of ; to suppress the default display. If you use the latter form, prefix it with k) in your post, so that others could easily cut and paste it in their q session.
q)k)+`a`b`c!(4 3 7 1 1;6 1 7 9 8;4 7 5 0 9)
a b c
-----
4 6 4
3 1 7
7 7 5
1 9 0
1 8 9What are the limits on the number of variables in q functions?¶
Reference: Lambdas
What does 'error mean?¶
Basics: Errors
Why does sg work with :: but not :? Also why does {x.time} not work?¶
Locals and globals are different: locals don’t have symbols associated with them, so for example .Q.dpft (you would have to pass in name of table) or x.time does not work with them. As a workaround for the second issue one can always use `time$x though.
How do I query a column of strings for multiple values?¶
If you wish to query a column of strings for a single value either like or ~ (Match) with an iterator can be used
q)e:([]c:("ams";"lon";"amS";"bar"))
q)select from e where c ~\:"ams"
c
-----
"ams"
q)select from e where c like "ams"
c
-----
"ams"
q)select from e where c like "am*"
c
-----
"ams"
"amS"To query for multiple strings you need to use another iterator, then aggregate the results into a single boolean value using sum or any. Generally the like form is easier to understand and more efficient.
q)select from e where any c like/:("lon";"am*")
c
-----
"ams"
"lon"
"amS"How to kill long/invalid query on a server?¶
You can achieve that by sending SIGINT to the server process. In *nix shell, try
$ kill -INT <pid>You can find the server process ID by examining .z.i.
How do I recall and edit keyboard input?¶
Start q under rlwrap to get readline support, e.g.
$ rlwrap l64/q -p 5001This is available in most Linux repositories.
An alternative to rlwrap is tecla's enhance. This is good for vi-mode users who would like more of vi’s keys functionality – eg d f x will delete everything up to the next x and you can paste it back, too.