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Viewing 13 posts - 16 through 28 (of 28 total)
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  • in reply to: 'nyi error #199

    admin
    Keymaster

    nyi = Not Yet Implemented
    Currently you can’t flip a keyed table in kdb, either use 0!t or () xkey t to remove the key and then flip the table.


    q)t:([a:1 2 3] b:`p`o`i)
    q)t
    a| b
    -| -
    1| p
    2| o
    3| i
    q)flip t
    'nyi

    q)flip 0!t
    a| 1 2 3
    b| p o i
    q)flip () xkey t
    a| 1 2 3
    b| p o i

    in reply to: delete variable and namespace #174

    admin
    Keymaster

    Mike,

    Unfortunately you cannot delete a namespace: http://www.timestored.com/kdb-guides/q-quirks#deleteNamespace

    You can delete all the variables contained in a namespace with
    delete from `.ns
    To delete from the default namespace:
    delete from `.

    in reply to: qsql select first last by group #173

    admin
    Keymaster

    Hi Dan,

    So here is the short qsql you mentioned for selecting the last entries by a grouping, simple “select by”:


    q)t:([] sym:`A`A`B`A`B`C`C`C; ex:`p`p`p`p`o`o`o`o; v:til 8; p:asc 8?100.)
    q)t
    sym ex v p
    -----------------
    A p 0 12.53237
    A p 1 16.94894
    B p 2 26.85287
    A p 3 37.97537
    B o 4 50.51764
    C o 5 56.72789
    ..
    q)select by sym from t
    sym| ex v p
    ---| -------------
    A | p 3 37.97537
    B | o 4 50.51764
    C | o 7 88.14778
    q)select by sym,ex from t
    sym ex| v p
    ------| ----------
    A p | 3 37.97537
    B o | 4 50.51764
    B p | 2 26.85287
    C o | 7 88.14778

    If we wrote this the long way and considered the parse tree:

    q)parse "select last v, last p by sym from t"
    ?
    `t
    ()
    (,`sym)!,`sym
    `v`p!((last;`v);(last;`p))

    We could create the functional query dynamically.
    We could then replace last with first, to dynamically generate and run our query.


    q){ [t; byCols] c:cols[t] except byCols; ?[t; (); ((),byCols)!(),byCols; c!{(last;x)} each c]} [`t; `sym]
    sym| ex v p
    ---| -------------
    A | p 3 37.97537
    B | o 4 50.51764
    C | o 7 88.14778

    q){ [t; byCols] c:cols[t] except byCols; ?[t; (); ((),byCols)!(),byCols; c!{(first;x)} each c]} [`t; `sym`ex]
    sym ex| v p
    ------| ----------
    A p | 0 12.53237
    B o | 4 50.51764
    B p | 2 26.85287
    C o | 5 56.72789

    Functional queries sometimes have their uses. Aaron Davies has some notes on them: http://www.q-ist.com/2013/03/my-kdb-user-meeting-presentation.html

    in reply to: reordering columns 'length error during xcols #171

    admin
    Keymaster

    The length error with xcols is being caused by your table being keyed. There’s no real reason for this other than that xcols currently does not support keyed tables. You can use either ` xkey t or the shortcut 0!t to unkey the table and then use xcols. e.g.

    q)t:2!([] date:.z.d+til 3; time:3?.z.t; sym:`p`o`i; price:1 2 3.; size:100*1 2 3)
    q)t
    date time | sym price size
    -----------------------| --------------
    2013.04.02 05:19:46.499| p 1 100
    2013.04.03 08:06:26.022| o 2 200
    2013.04.04 05:40:18.945| i 3 300
    q)`size`price xcols t / reproduce same length error
    k){(x,f@&~(f:cols y)in x)#y}
    'length
    #
    `size`price`date`time`sym
    (+`date`time!(2013.04.02 2013.04.03 2013.04.04;05:19:46.499 08:06:26.022 05:4..
    q.q))\

    q)0!t
    date time sym price size
    --------------------------------------
    2013.04.02 05:19:46.499 p 1 100
    2013.04.03 08:06:26.022 o 2 200
    2013.04.04 05:40:18.945 i 3 300

    q)`size`price xcols 0!t
    size price date time sym
    --------------------------------------
    100 1 2013.04.02 05:19:46.499 p
    200 2 2013.04.03 08:06:26.022 o
    300 3 2013.04.04 05:40:18.945 i

    in reply to: q language operator precedence #170

    admin
    Keymaster

    q code is has no order of precedence, it is interpreted from right to left. e.g.

    q)3%2-100+10*neg 11+3
    0.07142857
    q)3 % (2- (100+ (10*(neg (11+3)))))
    0.07142857

    in reply to: 'assign error #169

    admin
    Keymaster

    The assign error occurs when you try to assign a value to a kdb keyword. “type” is a reserved word. Notice your code works when I change that one word.


    q)UK_US_ORDERS:([] date:(); time:(); sym:(); size:(); price:(); TYPE:())
    q)UK_US_ORDERS
    date time sym size price TYPE
    -----------------------------
    q)

    It is possible to workaround this limitation to make your column named type but it would only leave your table extremely hard to query so it is not recommended.

    in reply to: save table as csv without headers #168

    admin
    Keymaster

    Hi Dan,

    An alternative method of saving a table is using 0:
    filehandle 0: “separator” 0: table

    For example:


    q)t
    sym time price size
    ------------------------------
    kjd 04:37:40.682 88.49717 28
    iik 07:54:24.777 66.8001 904
    oje 03:09:02.404 76.41439 511
    ndo 07:34:51.930 48.54351 139
    lkc 02:32:20.516 21.3479 775
    all 04:41:36.592 6.323408 353
    ..
    q)1_"," 0: t / convert to comma separated and drop first row
    "kjd,04:37:40.682,88.49717,28"
    "iik,07:54:24.777,66.8001,904"
    "oje,03:09:02.404,76.41439,511"
    "ndo,07:34:51.930,48.54351,139"
    "lkc,02:32:20.516,21.3479,775"
    "all,04:41:36.592,6.323408,353"
    "eln,02:16:35.865,75.98419,740"
    "bdi,10:33:07.085,6.746338,251"
    ..
    q)`:/temp/a.csv 0: 1_"," 0: t / save to file
    `:/temp/a.csv
    q)read0 `:/temp/a.csv / check what was written
    "kjd,04:37:40.682,88.49717,28"
    "iik,07:54:24.777,66.8001,904"
    "oje,03:09:02.404,76.41439,511"
    "ndo,07:34:51.930,48.54351,139"
    "lkc,02:32:20.516,21.3479,775"
    "all,04:41:36.592,6.323408,353"
    "eln,02:16:35.865,75.98419,740"
    "bdi,10:33:07.085,6.746338,251"
    ..

    in reply to: limit error #167

    admin
    Keymaster

    IPC transfer of data is limited to objects under 2GB in size, when an object is too large to transfer you will see a limit error.

    http://www.timestored.com/kdb-guides/kdb-database-limits#limit-error

    Try pulling the columns separately then join-each like so:


    q)a:h "select sym,time from t"; b:h "select price,size from t"; r:a,'b
    q)r
    sym time price size
    ------------------------------
    kjd 04:37:40.682 88.49717 28
    iik 07:54:24.777 66.8001 904
    oje 03:09:02.404 76.41439 511
    ndo 07:34:51.930 48.54351 139
    lkc 02:32:20.516 21.3479 775
    all 04:41:36.592 6.323408 353
    ..

    Be careful as if there is an insert between your calls, the join will fail with a length error. The alternative is to pull rows 0-50000, 50000-10000, 100000+ … in separate calls.

    in reply to: Greater precision in web browser #131

    admin
    Keymaster

    \P sets the precision of data shown throughout kdb.
    The number of decimal places shown for a floating point number can be adjusted as follows:


    q)\P
    7i
    q)1.10123010310312
    1.10123
    q)\P 15
    q)1.10123010310312
    1.10123010310312

    this controls the output to the web browser and saving csv’s etc.

    in reply to: return from function early #130

    admin
    Keymaster

    kdb supports the full range of execution controls, while, if, do, exceptions.

    Consider the following while loop:

    q){ i:0; while[i<5; show "hello ",string i; i+:1] }[]
    "hello 0"
    "hello 1"
    "hello 2"
    "hello 3"
    "hello 4"

    If we wanted to break from it early dependent on a condition we could do:

    q){ i:0; while[i<5; show "hello ",string i; if[i~3; :`p]; i+:1] }[]
    "hello 0"
    "hello 1"
    "hello 2"
    "hello 3"
    `p

    The single colon at :`p with nothing on the left is the equivalent of return in most other languages.

    Some more details on debugging and exceptions can be found at:
    http://www.timestored.com/kdb-guides/debugging-kdb

    in reply to: How do I time queries? #129

    admin
    Keymaster

    You can use \t to record how long a query takes:

    q)trade:`date xasc 100000?([] sym:1000?`RBS`o`i; size:1000?1000; price:1000?10.; date:1000?.z.d)
    q)select vwap:size wavg price by date from trade where sym =`RBS
    date | vwap
    ----------| ---------
    2000.01.10| 6.852109
    2000.01.18| 7.724738
    2000.01.22| 7.328888
    2000.01.30| 7.99496
    2000.02.08| 0.8450724
    2000.02.10| 0.276614
    ..
    q)\t select vwap:size wavg price by date from trade where sym =`RBS
    7
    q)\t select vwap:size wavg price by date from trade where sym =`RBS
    4

    To get a reliable timing use a do loop to repeat the action a number of times:

    q)\t do[100; select vwap:size wavg price by date from trade where sym =`RBS]
    238
    q)\t do[100; select vwap:size wavg price by date from trade where sym =`RBS]
    225

    \ts can be used to return both the time taken and the space used in bytes. Alternatively you can use the system format:

    q)\ts do[100; select vwap:size wavg price by date from trade where sym =`RBS]
    219 1772336
    q)system "ts do[100; select vwap:size wavg price by date from trade where sym =`RBS]"
    245 1772336

    in reply to: studio for kdb features #128

    admin
    Keymaster

    Good news qStudio 1.26 already supports both exporting to excel and row numbers on results.

    Simply right click on the result to export.

    in reply to: qStudio Roadmap #71

    admin
    Keymaster
Viewing 13 posts - 16 through 28 (of 28 total)