Hi all.
I’m looking improvements in my Kdb+ usage and I have question about segmentation.
Can segment name be used in query?
Eg we have X segments each Y rows and query require data only from one segment(we know from which).
Will kdb be looking data in all segments and it will X times slower than can be(if one thread used)?
Or we can use all information we know and search only in necessary segment?
Hi Vadim,
There was a discussion about this (or at least a similar issue) on the k4 listbox a few months back. The solution
is to just drop in the full path of the segment into your query. You will need to build a dictionary
that can map your query inputs to the correct segments.
e.g.
Suppose that you had some trades segmented by symbol range (A-M and N-Z) and then partitioned by date.
Instead of running a standard query like:
select from trades where date=2015.01.07, sym=`AAPL
you could run something along the lines of:
select from $":/AtoM/2015.01.07/trades" where sym=AAPL
The lookup of the segment could then be wrapped up into a function so that you could write something like:
select from findsegment[2015.01.07;AAPL;trades] where sym=`AAPL
Credit to Arthur Whitney and Pavel Hejbal on the k4 listbox for the solution!
http://www.listbox.com/member/archive/1080/2014/10/sort/time\_rev/page/5/entry/17:136/
Thanks
–
Mark Rooney
Financial Software Developer
AQUAQ Analytics
Thank Mark, it’s work (even w/o converting to sym `$“…”).
Not good that we can not use partition column in query, but it better than nothing.
1)I just curious if can I append string to text file without rewriting it fully?
q.Sync(“SymPathToString:{[SymPath]\r\n” +
“String: string SymPath;\r\n” +
“String: (1- count String)#String};”);
q.Sync(“saveSegment:{[SegmentName;hdbdir]\r\n” +
“SegmentPath: sv (hdbdir;dbdata;SegmentName);\r\n” +
“if[((.Q.P?SegmentPath)=(count .Q.P))=1b;ParPath: ` sv (hdbdir;`dbhead;`par.txt);ParPath 0: SymPathToString each (.Q.P,SegmentPath)]};”);
> can I append string to text file without rewriting it fully?
yes, certainly.
Thank, it’s look better.
Now I see strange :: after using my func for list of elements and no see them when use func once per time.
q.Sync("SymbolPathToString:{[SymbolPath]\r\n" + "String: string SymbolPath;\r\n" + "String: (1- count String)#String};"); q.Sync("SaveSegment:{[SegmentName;hdbdir]\r\n" + "SegmentPath: sv (hdbdir;dbdata;SegmentName);\r\n" + "if[((.Q.P?SegmentPath)=(count .Q.P))=1b;ParPath: sv (hdbdir;dbhead;par.txt); file: hopen ParPath; file (SymbolPathToString SegmentPath), "\n";hclose file]};");`
Hi Vadim,
That is expected behaviour when the last line of your function has a semi-colon at the end (generic null is returned).
Regards,
Meredith Grieve
Financial software developer
AquaQ Analytics
q)/ -returns a generic null (can’t see it on the command line)
q){x+1;} 2
q)/ -but the output is a generic null
q)(::) ~ {x+1;} 2
1b
q)/ -shows a list of generic nulls if you run function on a list using an adverb
q) {x+1;} each til 4
::
::
::
::
One simple question about functions syntax:
For example I have func:
f: {[arg1;arg2] 1 (string arg1), " ", (string arg2), "\n"}
and table :
table: ([] col1: foo1foo2foo3; col2: 100,101,102)`
How can I use each row of table on my func?
for single value vector I simple use:
f[foo;] each exec col2 from table`
but exec col1,col2 from table give me dictionary and I somehow should associate arg1, arg2 with col1,col2 of this dictionary.
Hey Vadim,
Try this… f’[tablecol1;tablecol2]
–
Glen Smith
Financial Software Developer
AQUAQ Analytics
Can it be hided?
anyway I’ll better replace :: to my output text -)
It got error, because tablecol1 and tablecol2 is vectors.
q)table:( col1: foo1foo2`foo3; col2: 100,101,102)
q)f: {[arg1;arg2] 1 (string arg1), " ", (string arg2), “\n”}
q)f’[tablecol1;tablecol2]
foo1 100
foo2 101
foo3 102
1 1 1
I don’t get an error. Did you leave the ’ out?
–
Glen Smith
Financial Software Developer
AQUAQ Analytics
Oh yes, thanks, I missed ’
Sadly that this approach works only for vectors.
table:([] col1: foo1foo2foo3; col2: 100,101,102)f: {[arg1;arg2;arg3] 1 (string arg1), " ", (string arg2), " ", (string arg3), “\n”}f’[xfoo;tablecol1;tablecol2] 'lenght
In my case only some of arguments will from tables and other will be constants.
f[`xfoo]'[table`col1;table`col2]
–
Glen Smith
Financial Software Developer
AQUAQ Analytics
Not sure that it works:
Your f function is incorrect
It should be f: {[arg1;arg2;arg3] 1 (string arg1), " ", (string arg2), " ", (string arg3), “\n”}
not It should be f: {[arg1;arg2;arg3] 1 (string arg1), " ", (string arg2), " ", (string arg3, “\n”)}
–
Glen Smith
Financial Software Developer
AQUAQ Analytics
or just use -1 instead and don’t bother with that new line append.
Thanks, my fault.
Sometimes is too hard to understand K syntax and not make any errors.
Mark’s links to the k4 listbox appear to be enticing non-licensed users to request access, so to clarify -
Please note that the kdb+/k4 listbox is a forum for _ licensed customers only _.
If you work at a company that has licensed kdb+, you may request to join the kdb+ Listbox by submitting your company email address via the link in the kdb+ listbox section at
Private email address (gmail, yahoo, hotmail etc) will not be considered for membership.
Non-licensed users should continue to use this google group.
thanks