Question

类型的函数 (Types of Functions)

功能可以以多种方式分类。 在这里，我们根据它们采用的参数的数量和类型以及结果类型对它们进行了分类。 功能可以，

• Atomic - 参数是原子的并产生原子结果

• Aggregate - 列表中的原子

• Uniform (list from list) - 扩展原子的概念，因为它们适用于列表。 参数列表的计数等于结果列表的计数。

• Other - 如果该功能不是来自上述类别。

数学中的二元运算在q中称为dyadic functions ; 例如，“+”。 类似地，一元操作称为monadic functions ; 例如，“abs”或“floor”。

常用函数 (Frequently Used Functions)

在q编程中经常使用很多函数。 在这一节中，我们将看到一些流行功能的用法 -

abs

q) abs -9.9/Absolute value, Negates -ve number & leaves non -ve number
9.9

all

q) all 4 5 0 -4/Logical AND (numeric min), returns the minimum value
0b

最大（＆），最小（|）和不（！）

q) /And, Or, and Logical Negation
q) 1b & 1b       /And (Max)
1b
q) 1b|0b             /Or (Min)
1b
q) not 1b             /Logical Negate (Not)
0b 

asc

q)asc 1 3 5 7 -2 0 4   /Order list ascending, sorted list
                       /in ascending order i
s returned
`s#-2 0 1 3 4 5 7
q)/attr - gives the attributes of data, which describe how it's sorted.
`s denotes fully sorted, `u denotes unique and `p and `g are used to 
refer to lists with repetition, with `p standing for parted and `g for grouped

avg

q)avg 3 4 5 6 7          /Return average of a list of numeric values
5f
q)/Create on trade table
q)trade:([]time:3?(.z.Z-200);sym:3?(`ibm`msft`apple);price:3?99.0;size:3?100)

by

q)/ by - Groups rows in a table at given sym
q)select sum price by sym from trade   /find total price for each sym
  sym  |   price
------ | --------
 apple | 140.2165
  ibm  | 16.11385

cols

q)cols trade/Lists columns of a table
`time`sym`price`size

计数

q)count (til 9)/Count list, count the elements in a list and
               /return a single int value 9

port

q)\p 9999/assign port number
q)/csv - This command allows queries in a browser to be exported to
   excel by prefixing the query, such as http://localhost:9999/.csv?select from trade where sym =`ibm

cut

q)/ cut - Allows a table or list to be cut at a certain point
q)(1 3 5) cut "abcdefghijkl"
                           /the argument is split at 1st, 3rd and 5th letter.
"bc"
"de"
"fghijkl"
q)5 cut "abcdefghijkl"     /cut the right arg. Into 5 letters part
                           /until its end.
"abcde"
"fghij"
"kl"

删除 (Delete)

q)/delete - Delete rows/columns from a table
q)delete price from trade
          time              sym   size
---------------------------------------
  2009.06.18T06:04:42.919  apple   36
  2009.11.14T12:42:34.653   ibm    12
  2009.12.27T17:02:11.518  apple   97

Distinct

q)/distinct - Returns the distinct element of a list
q)distinct 1 2 3 2 3 4 5 2 1 3           /generate unique set of number
1 2 3 4 5

enlist

q)/enlist - Creates one-item list.
q)enlist 37
,37
q)type 37          /-ve type value
-7h
q)type enlist 37   /+ve type value
7h 

Fill (^)

q)/fill - used with nulls. There are three functions for processing null values.
The dyadic function named fill replaces null values in the right argument with the atomic left argument.
q)100 ^ 3 4 0N 0N -5
3 4 100 100 -5
q)`Hello^`jack`herry``john`
`jack`herry`Hello`john`Hello

Fills

q)/fills - fills in nulls with the previous not null value.
q)fills 1 0N 2 0N 0N 2 3 0N -5 0N
1 1 2 2 2 2 3 3 -5 -5

First

q)/first - returns the first atom of a list
q)first 1 3 34 5 3
1

Flip

q)/flip - Monadic primitive that applies to lists and associations. It interchange the top two levels of its argument.
q)trade
       time                   sym      price   size
------------------------------------------------------
  2009.06.18T06:04:42.919    apple   72.05742   36
  2009.11.14T12:42:34.653    ibm     16.11385   12
  2009.12.27T17:02:11.518    apple   68.15909   97
q)flip trade
time | 2009.06.18T06:04:42.919 2009.11.14T12:42:34.653
2009.12.27T17:02:11.518
sym   |  apple         ibm         apple
price | 72.05742     16.11385    68.15909
size  | 36 12 97

iasc

q)/iasc - Index ascending, return the indices of the ascended sorted list relative to the input list.
q)iasc 5 4 0 3 4 9
2 3 1 4 0 5

Idesc

q)/idesc - Index desceding, return the descended sorted list relative to the input list
q)idesc 0 1 3 4
3 2 1 0

in

q)/in - In a list, dyadic function used to query list (on the right-handside) about their contents.
q)(2 4) in 1 2 3
10b

插入

q)/insert - Insert statement, upload new data into a table.
q)insert[`trade;((.z.Z);`samsung;48.35;99)],3
q)trade
      time                  sym       price     size
------------------------------------------------------
 2009.06.18T06:04:42.919   apple    72.05742     36
 2009.11.14T12:42:34.653    ibm     16.11385     12
 2009.12.27T17:02:11.518   apple    68.15909     97
 2015.04.06T10:03:36.738   samsung  48.35        99

key

q)/key - three different functions i.e. generate +ve integer number, gives content of a directory or key of a table/dictionary.
q)key 9
0 1 2 3 4 5 6 7 8
q)key `:c:
`$RECYCLE.BIN`Config.Msi`Documents and Settings`Drivers`Geojit`hiberfil.sys`I..

lower

q)/lower - Convert to lower case and floor
q)lower ("JoHn";`HERRY`SYM)
"john"
`herry`sym

最大和最小（即|和＆）

q)/Max and Min/a|b and a&b
q)9|7
9
q)9&5
5

null

q)/null - return 1b if the atom is a null else 0b from the argument list
q)null 1 3 3 0N
0001b

Peach

q)/peach - Parallel each, allows process across slaves
q)foo peach list1      /function foo applied across the slaves named in list1
'list1
q)foo:{x+27}
q)list1:(0 1 2 3 4)
q)foo peach list1      /function foo applied across the slaves named in list1
27 28 29 30 31

Prev

q)/prev - returns the previous element i.e. pushes list forwards
q)prev 0 1 3 4 5 7
0N 0 1 3 4 5

Random( ?)

q)/random - syntax - n?list, gives random sequences of ints and floats
q)9?5
0 0 4 0 3 2 2 0 1
q)3?9.9
0.2426823 1.674133 3.901671

Raze

q)/raze - Flattn a list of lists, removes a layer of indexing from a list of lists. for instance:
q)raze (( 12 3 4; 30 0);("hello";7 8); 1 3 4)
12 3 4
30 0
"hello"
7 8
1
3
4

read0

q)/read0 - Read in a text file
q)read0 `:c:/q/README.txt   /gives the contents of *.txt file

read1

q)/read1 - Read in a q data file
q)read1 `:c:/q/t1
0xff016200630b000500000073796d0074696d6500707269636…

reverse

q)/reverse - Reverse a list
q)reverse 2 30 29 1 3 4
4 3 1 29 30 2
q)reverse "HelloWorld"
"dlroWolleH"

set

q)/set - set value of a variable
q)`x set 9
`x
q)x
9
q)`:c:/q/test12 set trade
`:c:/q/test12
q)get `:c:/q/test12
       time                   sym      price     size
---------------------------------------------------------
  2009.06.18T06:04:42.919    apple    72.05742    36
  2009.11.14T12:42:34.653     ibm     16.11385    12
  2009.12.27T17:02:11.518    apple    68.15909    97
  2015.04.06T10:03:36.738    samsung  48.35       99
  2015.04.06T10:03:47.540    samsung  48.35       99
  2015.04.06T10:04:44.844    samsung  48.35       99

ssr

q)/ssr - String search and replace, syntax - ssr["string";searchstring;replaced-with]
q)ssr["HelloWorld";"o";"O"]
"HellOWOrld"

串

q)/string - converts to string, converts all types to a string format.
q)string (1 2 3; `abc;"XYZ";0b)
(,"1";,"2";,"3")
"abc"
(,"X";,"Y";,"Z")
,"0"

SV

q)/sv - Scalar from vector, performs different tasks dependent on its arguments.
It evaluates the base representation of numbers, which allows us to calculate the number of seconds in a month or convert a length from feet and inches to centimeters.
q)24 60 60 sv 11 30 49
41449  /number of seconds elapsed in a day at 11:30:49

system

q)/system - allows a system command to be sent,
q)system "dir *.py"
" Volume in drive C is New Volume"
" Volume Serial Number is 8CD2-05B2"
""
" Directory of C:\\Users\\myaccount-raj"
""
"09/14/2014    06:32 PM     22 hello1.py"
"                1 File(s)    22 bytes"

tables

q)/tables - list all tables
q)tables `
`s#`tab1`tab2`trade

Til

q)/til - Enumerate
q)til 5
0 1 2 3 4

trim

q)/trim - Eliminate string spaces
q)trim " John "
"John"

vs

q)/vs - Vector from scaler , produces a vector quantity from a scaler quantity
q)"|" vs "20150204|msft|20.45"
"20150204"
"msft"
"20.45"

xasc

q)/xasc - Order table ascending, allows a table (right-hand argument) to be sorted such that (left-hand argument) is in ascending order
q)`price xasc trade
          time                 sym      price      size
----------------------------------------------------------
   2009.11.14T12:42:34.653     ibm     16.11385     12
   2015.04.06T10:03:36.738   samsung   48.35        99
   2015.04.06T10:03:47.540   samsung   48.35        99
   2015.04.06T10:04:44.844   samsung   48.35        99
   2009.12.27T17:02:11.518    apple    68.15909     97
   2009.06.18T06:04:42.919    apple    72.05742     36

xcol

q)/xcol - Renames columns of a table
q)`timeNew`symNew xcol trade
        timeNew                 symNew    price      size
-------------------------------------------------------------
   2009.06.18T06:04:42.919      apple    72.05742     36
   2009.11.14T12:42:34.653       ibm     16.11385     12
   2009.12.27T17:02:11.518      apple    68.15909     97
   2015.04.06T10:03:36.738     samsung   48.35        99
   2015.04.06T10:03:47.540     samsung   48.35        99
   2015.04.06T10:04:44.844     samsung   48.35        99

xcols

q)/xcols - Reorders the columns of a table,
q)`size`price xcols trade
  size    price           time                   sym
-----------------------------------------------------------
   36   72.05742   2009.06.18T06:04:42.919      apple 
   12   16.11385   2009.11.14T12:42:34.653       ibm
   97   68.15909   2009.12.27T17:02:11.518      apple
   99   48.35      2015.04.06T10:03:36.738     samsung 
   99   48.35      2015.04.06T10:03:47.540     samsung
   99   48.35      2015.04.06T10:04:44.844     samsung

xdesc

q)/xdesc - Order table descending, allows tables to be sorted such that the left-hand argument is in descending order.
q)`price xdesc trade
        time                   sym       price      size
-----------------------------------------------------------
   2009.06.18T06:04:42.919    apple    72.05742      36
   2009.12.27T17:02:11.518    apple    68.15909      97
   2015.04.06T10:03:36.738   samsung   48.35         99
   2015.04.06T10:03:47.540   samsung   48.35         99
   2015.04.06T10:04:44.844   samsung   48.35         99
   2009.11.14T12:42:34.653     ibm     16.11385      12

xgroup

q)/xgroup - Creates nested table
q)`x xgroup ([]x:9 18 9 18 27 9 9;y:10 20 10 20 30 40)
'length
q)`x xgroup ([]x:9 18 9 18 27 9 9;y:10 20 10 20 30 40 10)
  x  |    y
---- | -----------
  9  | 10 10 40 10
  18 | 20 20
  27 | ,30

xkey

q)/xkey - Set key on table
q)`sym xkey trade
    sym   |      time                    price     size
--------- | -----------------------------------------------
   apple  | 2009.06.18T06:04:42.919    72.05742     36
    ibm   | 2009.11.14T12:42:34.653    16.11385     12
   apple  | 2009.12.27T17:02:11.518    68.15909     97
  samsung | 2015.04.06T10:03:36.738    48.35        99
  samsung | 2015.04.06T10:03:47.540    48.35        99
  samsung | 2015.04.06T10:04:44.844    48.35        99

System Commands

系统命令控制q环境。 它们具有以下形式 -

\cmd [p]       where p may be optional

下面讨论了一些流行的系统命令 -

\a [namespace] - 列出给定命名空间中的表

q)/Tables in default namespace
q)\a
,`trade
q)\a .o        /table in .o namespace.
,`TI

\b - 查看依赖项

q)/ views/dependencies
q)a:: x+y     /global assingment
q)b:: x+1
q)\b
`s#`a`b

\B - 待定视图/依赖项

q)/ Pending views/dependencies
q)a::x+1    /a depends on x
q)\B        /the dependency is pending
'/the dependency is pending
q)\B
`s#`a`b
q)\b
`s#`a`b
q)b
29
q)a
29
q)\B
`symbol$()

\cd - 更改目录

q)/change directory, \cd [name]
q)\cd
"C:\\Users\\myaccount-raj"
q)\cd ../new-account
q)\cd
"C:\\Users\\new-account"

\d - 设置当前命名空间

q)/ sets current namespace \d [namespace]
q)\d             /default namespace
'
q)\d .o          /change to .o
q.o)\d
`.o
q.o)\d .        /return to default
q)key `          /lists namespaces other than .z
`q`Q`h`j`o
q)\d .john       /change to non-existent namespace
q.john)\d
`.john
q.john)\d .
q)\d
`.

\l - 从db加载文件或目录

q)/ Load file or directory, \l
q)\l test2.q/loading test2.q which is stored in current path.
   ric      |     date      ex      openP    closeP    MCap
----------- | -------------------------------------------------
 JPMORGAN   | 2008.05.23  SENSEX  18.30185  17.16319  17876
   HSBC     | 2002.05.21  NIFTY   2.696749  16.58846  26559
 JPMORGAN   | 2006.09.07  NIFTY   14.15219  20.05624  14557
   HSBC     | 2010.10.11  SENSEX  7.394497  25.45859  29366
 JPMORGAN   | 2007.10.02  SENSEX  1.558085  25.61478  20390
   ric     |    date       ex      openP     closeP    MCap
---------- | ------------------------------------------------
  INFOSYS  | 2003.10.30    DOW    21.2342   7.565652   2375
 RELIANCE  | 2004.08.12    DOW    12.34132  17.68381   4201
   SBIN    | 2008.02.14    DOW    1.830857  9.006485   15465
  INFOSYS  | 2009.06.11  HENSENG  19.47664  12.05208   11143
   SBIN    | 2010.07.05    DOW    18.55637  10.54082   15873

\p - 端口号

q)/ assign port number, \p
q)\p
5001i
q)\p 8888
q)\p
8888i

\\ - 从q控制台退出

\\ - exit
Exit form q.