[R] Multiplying each row of a big matrix with a vector

Wed Jan 30 12:47:24 CET 2008

I understood that you only need to multiply each row of Ret by the
vector Pos but it seems that you would like to sum the resulting vector
element in order to have a vector of length 500. 
That is merely the matrix multiplication in R!!! 
i.e.  Ret %*% Pos. 
Am I getting the question wrong? 

Mama 

-----
Mama Attiglah, PhD
Advanced Research Center
Quantitative Research Analyst
State Street Bank
+44(0)20 7698 6290 (Direct Line)
+44 (0)207 004 2968 (Direct Fax)
Please visit our Web site at 
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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Attiglah, Mama
Sent: 30 January 2008 11:32
To: Megh Dal; r-help at stat.math.ethz.ch
Subject: Re: [R] Multiplying each row of a big matrix with a vector

Ret= matrix(sample( 1:1000, 500*9), nrow=500, ncol=9)

Pos= c(  2593419  ,2130220,  6198197,  1673888,  1980000 , 1784732 ,
2052120 ,-7490228 ,-5275000)

Solution = Ret * matrix( rep(Pos, 500), nrow=500, byrow=TRUE)
Use the element-wise multiplication rather than a matrix multiplication.
Hope this helps.
Mama 

-----
Mama Attiglah, PhD
Advanced Research Center
Quantitative Research Analyst
State Street Bank
+44(0)20 7698 6290 (Direct Line)
+44 (0)207 004 2968 (Direct Fax)
Please visit our Web site at 
www.ssga.com

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Megh Dal
Sent: 30 January 2008 07:20
To: r-help at stat.math.ethz.ch
Subject: [R] Multiplying each row of a big matrix with a vector

I have a big matrix 'ret'. I want to multiply each row of it with a 2nd
vector 'pos', resulting result, I want to save in a vector named 'port'.
I wrote following code:

  > pos
[1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120
-7490228 -5275000

  > dim(ret)
[1] 500   9

  > fu    # user defined function
function(x)
   {
    fu = x %*% t(pos)
   }
port = apply(ret, 1, fu)

  > dim(port)
[1]  81 500

  My desire is to get port as a vector with length 500. However I am not
getting that?

  Can anyone tell me how to correct that? 

  Regards,

---------------------------------

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