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Types of Functions
Functions can be classified in a number of ways. Here we have classified them based on the number and type of argument they take and the result type. Functions can be,
-
Atomic − Where the arguments are atomic and produce atomic results
-
Aggregate − atom from list
-
Uniform (list from list) − Extended the concept of atom as they apply to lists. The count of the argument list equals the count of the result list.
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Other − if the function is not from the above category.
Binary operations in mathematics are called dyadic functions in q; for example, “+”. Similarly unary operations are called monadic functions; for example, “abs” or “floor”.
Frequently Used Functions
There are quite a few functions used frequently in q programming. Here, in this section, we will see the usage of some popular functions −
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
Max (&), Min (|), and Not (!)
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
count
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"
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
insert
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
Max and Min (i.e. | and &)
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"
string
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
System commands control the q environment. They are of the following form −
cmd [p] where p may be optional
Some of the popular system commands have been discussed below −
a [ namespace] – List tables in the given namespace
q)/Tables in default namespace q)a ,`trade q)a .o / table in .o namespace. ,`TI
b – View dependencies
q)/ views/dependencies q)a:: x+y / global assingment q)b:: x+1 q)b `s#`a`b
B – Pending views / dependencies
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 – Change directory
q)/change directory, cd [name] q)cd "C:\Users\myaccount-raj" q)cd ../new-account q)cd "C:\Users\new-account"
d – sets current namespace
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 – load file or directory from db
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 – port number
q)/ assign port number, p q)p 5001i q)p 8888 q)p 8888i
\ – Exit from q console
\ - exit Exit form q.
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