📅 最后修改于: 2020-11-03 06:50:25 🧑 作者: Mango
可以通过多种方式对功能进行分类。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。功能可以是，
原子-参数是原子的并产生原子结果
聚集-列表中的原子
统一(列表中的列表) -扩展了原子应用于列表的概念。参数列表的数量等于结果列表的数量。
其他-如果函数不是来自上述类别。
数学中的二元运算在q中称为二进位函数；例如“ +”。同样，一元运算也称为单子函数；例如“ abs”或“ floor”。
q编程中经常使用很多功能。在本节中，我们将看到一些常用功能的用法-
q) abs -9.9 / Absolute value, Negates -ve number & leaves non -ve number
9.9
q) all 4 5 0 -4 / Logical AND (numeric min), returns the minimum value
0b
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
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
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)
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
q)cols trade / Lists columns of a table
`time`sym`price`size
q)count (til 9) / Count list, count the elements in a list and
/ return a single int value 9
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
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"
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
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
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
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
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
q)/first - returns the first atom of a list
q)first 1 3 34 5 3
1
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
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
q)/idesc - Index desceding, return the descended sorted list relative to the input list
q)idesc 0 1 3 4
3 2 1 0
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
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
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..
q)/lower - Convert to lower case and floor
q)lower ("JoHn";`HERRY`SYM)
"john"
`herry`sym
q)/Max and Min / a|b and a&b
q)9|7
9
q)9&5
5
q)/null - return 1b if the atom is a null else 0b from the argument list
q)null 1 3 3 0N
0001b
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
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
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
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
q)/read0 - Read in a text file
q)read0 `:c:/q/README.txt / gives the contents of *.txt file
q)/read1 - Read in a q data file
q)read1 `:c:/q/t1
0xff016200630b000500000073796d0074696d6500707269636…
q)/reverse - Reverse a list
q)reverse 2 30 29 1 3 4
4 3 1 29 30 2
q)reverse "HelloWorld"
"dlroWolleH"
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
q)/ssr - String search and replace, syntax - ssr["string";searchstring;replaced-with]
q)ssr["HelloWorld";"o";"O"]
"HellOWOrld"
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"
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
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"
q)/tables - list all tables
q)tables `
`s#`tab1`tab2`trade
q)/til - Enumerate
q)til 5
0 1 2 3 4
q)/trim - Eliminate string spaces
q)trim " John "
"John"
q)/vs - Vector from scaler , produces a vector quantity from a scaler quantity
q)"|" vs "20150204|msft|20.45"
"20150204"
"msft"
"20.45"
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
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
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
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
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
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
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-
q)/Tables in default namespace
q)\a
,`trade
q)\a .o / table in .o namespace.
,`TI
q)/ views/dependencies
q)a:: x+y / global assingment
q)b:: x+1
q)\b
`s#`a`b
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$()
q)/change directory, \cd [name]
q)\cd
"C:\\Users\\myaccount-raj"
q)\cd ../new-account
q)\cd
"C:\\Users\\new-account"
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
`.
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
q)/ assign port number, \p
q)\p
5001i
q)\p 8888
q)\p
8888i
\\ - exit
Exit form q.