[R] "ciclo for" in matrix construction ( matlab -> R )

[Massimo Di Stefano]

hi,
i'm new to R
i have a little script in matlab....
now i'm porting it to R but i've some problem.
how can i write in R language this
matlab/octave code:

LX = L ;                     >>> L is a matrix
ss = size(LX,1);
E_N_2 = zeros(ss,2);

for i = 1:ss
E_2 = E_0 + LX(i,1)*C(3)+LX(i,2)*C(4);      >>>> E_0 , C(3), c(4)  
are costant
N_2 = N_0 + LX(i,2)*C(3)-LX(i,1)*C(4);
r=[ E_2,N_2];
E_N_2(i,:)=r;
end
E_N_2

i'm try so :

library(matlab)
LX <- L
ss <- dim(LX)
ss <- ss[1]
E_N_2 <- zeros(ss,2)
for(i in 1:ss)
.....
.....?

thanks for any help :-)
Massimo

my mayor problem is to know how the "cicle for" works
        [[alternative HTML version deleted]]

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[cberry]

The help page for 'for' warns:

      Note that it is a common mistake to forget to put braces ('{ ..
      }') around your statements, e.g., after 'if(..)' or 'for(....)'.
      In particular, you should not have a newline between '}' and
      'else' to avoid a syntax error in entering a 'if ... else'
      construct at the keyboard or via 'source'. For that reason, one
      (somewhat extreme) attitude of defensive programming is to always
      use braces, e.g., for 'if' clauses.

Also this is illustrated in R FOR OCTAVE USERS

  http://cran.r-project.org/doc/contrib/R-and-octave.txt

in the section starting:

  MULTILINE FOR STATEMENTS:



On Wed, 4 Oct 2006, massimodisasha wrote:

> hi,
> i'm new to R
> i have a little script in matlab....
> now i'm porting it to R but i've some problem.
> how can i write in R language this
> matlab/octave code:
>
> LX = L ;                     >>> L is a matrix
> ss = size(LX,1);
> E_N_2 = zeros(ss,2);
>
> for i = 1:ss
> E_2 = E_0 + LX(i,1)*C(3)+LX(i,2)*C(4);      >>>> E_0 , C(3), c(4)
> are costant
> N_2 = N_0 + LX(i,2)*C(3)-LX(i,1)*C(4);
> r=[ E_2,N_2];
> E_N_2(i,:)=r;
> end
> E_N_2
>
> i'm try so :
>
> library(matlab)
> LX <- L
> ss <- dim(LX)
> ss <- ss[1]
> E_N_2 <- zeros(ss,2)
> for(i in 1:ss)
> .....
> .....?
>
> thanks for any help :-)
> Massimo
>
> my mayor problem is to know how the "cicle for" works
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Charles C. Berry                        [phone]
                                          Dept of Family/Preventive Medicine
E mailto:[hidden email]         UC San Diego
http://biostat.ucsd.edu/~cberry/         La Jolla, San Diego 92093-0717

______________________________________________
[hidden email] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

[Jeff Newmiller]

massimodisasha wrote:

> hi,
> i'm new to R
> i have a little script in matlab....
> now i'm porting it to R but i've some problem.
> how can i write in R language this
> matlab/octave code:
>
> LX = L ;                     >>> L is a matrix
> ss = size(LX,1);
> E_N_2 = zeros(ss,2);
>
> for i = 1:ss
> E_2 = E_0 + LX(i,1)*C(3)+LX(i,2)*C(4);      >>>> E_0 , C(3), c(4)  
> are costant
> N_2 = N_0 + LX(i,2)*C(3)-LX(i,1)*C(4);
> r=[ E_2,N_2];
> E_N_2(i,:)=r;
> end
> E_N_2
>
> i'm try so :
>
> library(matlab)
> LX <- L
> ss <- dim(LX)
> ss <- ss[1]
> E_N_2 <- zeros(ss,2)
> for(i in 1:ss)
> .....
> .....?
>
> thanks for any help :-)
> Massimo
>
> my mayor problem is to know how the "cicle for" works

Perhaps a more important problem is learning how to
use matrix algebra.  Loops are notoriously slow in R,
and worth avoiding in octave as well.

E_0 <- 12
N_0 <- 13
C3 <- 21
C4 <- 22
L <- matrix(c(1,2,3,4,5,6,7,8,9),ncol=3)

ss <- dim(L)[1]
LX <- L[1:ss,1:2]
C <- matrix(c(C3,C4,-C4,C3),ncol=2)
EN <- matrix(rep(c(E_0,N_0),ss),ncol=2,byrow=TRUE)
E_N_2 <- EN + LX %*% C
E_N_2


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[hidden email] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.