[R] help with table partition

[davidr at rhotrading.com]

apply(log(P), 2, diff)

David L. Reiner
Rho Trading Securities, LLC
Chicago  IL  60605
312-362-4963

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Wong, Kim
Sent: Thursday, June 15, 2006 11:30 AM
To: Petr Pikal; Jacques VESLOT
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] help with table partition


Hi, thank you all for the help.

The split function works very well.

I have an additional question.  If I have a matrix of prices (row = 30,
col = 2) in matrix P

P:

30 40
31.5 42
....
....
....

32 43

What is the quickest way to get a new matrix, where each entry is the
ln(Pt/Pt-1)?

I have no prob doing this using a loop, but that might not be most
efficient if my table is huge.  Moreover, I've read the apply/lapply
functions, but I could not get the right parameters to use.

Thank you all for help.
K.


-----Original Message-----
From: Petr Pikal [mailto:petr.pikal at precheza.cz] 
Sent: Thursday, June 15, 2006 10:35 AM
To: Wong, Kim
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] help with table partition

Hi

maybe ?split and ?t is what you want

mat<-matrix(rnorm(1000), 100,10)

mat.s<-split(data.frame(mat), rep(1:5, each=20)) 
#splits mat to list with 5 eqal submatrices

lapply(mat.s,t)
# transpose matrices in list

gives you a list of transposed tables, which is probably better than 
separate tables. Just change rep(1:5,each=20) to rep (1:170, 
each=366).

or
a quicker one without data frame

mat <- matrix(rnorm(62220*73), 62220,73)

dim(mat) <- c(366,73,170)
mat.i <- array(0,dim=c(73,366,170))
for (i in 1:170) mat[ , , i] <- t(mat[ , , i])

HTH
Petr





On 15 Jun 2006 at 9:38, Wong, Kim wrote:

Date sent:      	Thu, 15 Jun 2006 09:38:29 -0400
From:           	"Wong, Kim" <kwong at nymex.com>
To:             	<r-help at stat.math.ethz.ch>
Subject:        	[R] help with table partition

> Hi,
> 
> 
> 
> I have a test_table where the dim is 62220 by 73 (row by col)
> 
> 
> 
> I would like to partition the rows into 170 equal parts (170 tables
> where each is of dim 366 by 73), and rearrange them horizontally. The
> source codes I have:
> 
> 
> 
> for (i in 1:170) {
> 
>             c = cbind(c,test_table[(367*i+1):(367*(i+1)),2:73]);
> 
>       }
> 
> 
> 
> Unfortunately, using for loop and cbind for a table of this size
> causes long running time.  What is the most efficient way to get the
> table that I want? 
> 
> 
> 
> Thanks for any help.
> 
> K.
> 
> 
> 
> 
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Petr Pikal
petr.pikal at precheza.cz


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