R client for kdb+

Execute kdb+ queries from R for advanced high-performance analytics.

See Interfacing with R on Kx wiki.

Installation

# remove old package
if('qserver' %in% rownames(installed.packages())) remove.packages('qserver')
# install devtools
if(! 'devtools' %in% rownames(installed.packages())) install.packages('devtools')
library(devtools)
# install rkdb
devtools::install_github('kxsystems/rkdb', quiet=TRUE)
# to install rkdb of perticular release
# devtools::install_github('kxsystems/[email protected]', quiet=TRUE)
library(rkdb)

First steps

Open a q server and connect to it

Open a qserver to test the installation

q -p 5000

Open a connection to it

h <- open_connection('localhost',5000) #this open a connection

Hello kdb

You can evaluate any kdb expression and its result will come back to R:

execute(h, '1+1')

## [1] 2

Assigning a variable in q workspace also works:

execute(h, 'x:1+1') #assign x hopefully to 2

## NULL

execute(h, 'x') # get back the value

## [1] 2

Getting data from kdb to R

As per Q for mortals kdb uses some basic types that might not have a direct equivalent in R. Note also that this is not a bijective operation. The conversions (from kdb to R, at time of writing) are:

kdb/q	r
boolean	logical
byte	integer
short	integer
int	integer
long	numeric
real	numeric
float	numeric
char	character
symbol	character
timestamp	POSIXct
month	integer
date	Date
datetime	POSIXct
timespan	difftime
minute	difftime
second	difftime
time	integer
enumeration	character
table	data.frame
keyed table	data.frame
dictionary (mixed types)	named list
dictionary (same types)	named vector
function	character
list (same types)	vector
list (same 'complex' types)	list
list (different types)	list

Computing on kdb

rkdb provides a convienient way to retrieve computation done on the kdb side so you can have the best of both worlds:

kdb <- '
t: ([] x:1000#`a`b`c;y:1000#1f*til 10;z:1000#1f*til 4);
select sum y, dev z by x from t
'

execute(h, kdb)

##   x    y        z
## 1 a 1503 1.120709
## 2 b 1497 1.116689
## 3 c 1500 1.116689

One can for instance use R graphical capabilities:

kdb <- '
t: ([] x:1000#`a`b`c;y:1000#1f*til 10;z:1000#1f*til 4);
select y,z from t where x=`a
'

DF <- execute(h, kdb)
plot(DF$y, DF$z, main='scatter plot', xlab='y values', ylab='z values')

Getting data from R to kdb

Evaluating kdb expressions using R objects

You can call kdb functions on R objects, those will be passed/converted to the kdb side, and the kdb expression will be evaluated:

execute(h, "raze", list(c(1,2,3), c(4,5,6)))

## [1] 1 2 3 4 5 6

execute(h, "+", 2, 5)

## [1] 7

execute(h,'{`tmp set x}',data.frame(a=c(1,2,3),b=c("a","b","b")))

## [1] "tmp"

As an example here is how you can use the left-join function on 2 data.frames:

DF1 <- data.frame(x=c('x','x','y','y'), y=1:4)
DF2 <- data.frame(x=c('x','y','z'), z=seq(10,30,10))
execute(h, "{[x;y] x lj `x xkey y}", DF1, DF2)

##   x y  z
## 1 x 1 10
## 2 x 2 10
## 3 y 3 20
## 4 y 4 20