# specific matrix element tranformation

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## specific matrix element tranformation

 Hi guys, I am trying to write a function that allows me to perform specific transformations to each element of a 2 by 2 matrix to generate a 3 by 3 matrix. Input into function-2 by 2 matrix Output from function -3 by 3 matrix For example: # a is my original 2 by 2 matrix #b is my new 3 by 3 matrix set.seed(2) a=matrix(rnorm(4),ncol=2) #let's say these are the transformations i wish to perform b[1,1]=a[1,1]+1 b[1,2]=a[2,1]*a[2,2] b[1,3]=a[2,2]+a[1,1] b[2,1]=a[1,1]-5 b[2,2]=sqrt(a[2,2]) b[2,3]=a[1,1]/a[2,2] b[3,1]=a[2,2]-3 b[3,2]=a[1,1]*[a[1,2]+a[2,2]) b[3,3]=sqrt(a[1,1])/a[1,2]) Thanks. Cheers, B
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## Re: specific matrix element tranformation

 Hi guys, After a long while I came up with this : set.seed(2) a<-matrix(rnorm(4),ncol=2) abc<-function(a) { b=matrix(NA,nrow=3,ncol=3) b[1,1]=a[1,1]+1 b[1,2]=a[2,1]*a[2,2] b[1,3]=a[2,2]+a[1,1] b[2,1]=a[1,1]-5 b[2,2]=sqrt(a[2,2]) b[2,3]=a[1,1]/a[2,2] b[3,1]=a[2,2]-3 b[3,2]=a[1,1]*(a[1,2]+a[2,2]) b[3,3]=sqrt(a[1,1])/a[1,2] return(b=matrix(c(b[1,1],b[1,2],b[1,3],b[2,1],b[2,2],b[2,3], b[3,1],b[3,2],b[3,3]),ncol=3)) } How can I improve on it? Cheers, B
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## Re: specific matrix element tranformation

 Hello, Inline Em 17-08-2012 04:39, bantex escreveu: > Hi guys, > > After a long while I came up with this : > > set.seed(2) > a<-matrix(rnorm(4),ncol=2) > abc<-function(a) > { > b=matrix(NA,nrow=3,ncol=3) > b[1,1]=a[1,1]+1 > b[1,2]=a[2,1]*a[2,2] > b[1,3]=a[2,2]+a[1,1] > b[2,1]=a[1,1]-5 > b[2,2]=sqrt(a[2,2]) > b[2,3]=a[1,1]/a[2,2] > b[3,1]=a[2,2]-3 > b[3,2]=a[1,1]*(a[1,2]+a[2,2]) > b[3,3]=sqrt(a[1,1])/a[1,2] > > return(b=matrix(c(b[1,1],b[1,2],b[1,3],b[2,1],b[2,2],b[2,3], > b[3,1],b[3,2],b[3,3]),ncol=3)) You don't need to say that 'b' is a matrix a second time! And this form is wrong, you should add 'byrow = TRUE' since you're using row order. > } > > How can I improve on it? With your data, you would have two errors in applying function abc to matrix 'a'. Try the following. fun <- function(a){      b <- matrix(nrow = 3, ncol = 3)      #let's say these are the transformations i wish to perform      b[1,1] <- a[1,1]+1      b[1,2] <- a[2,1]*a[2,2]      b[1,3] <- a[2,2]+a[1,1]      b[2,1] <- a[1,1]-5      if(a[2,2] < 0){          warning("a[2, 2] is negative, using zero for its square root b[2,2].")          b[2,2] <- 0      }else{          b[2,2] <- sqrt(a[2,2])      }      if(a[2,2] == 0){          warning("a[2, 2] is zero, using zero for division result b[2,3].")          b[2,3] <- 0      }else{          b[2,3] <- a[1,1]/a[2,2]      }      b[3,1] <- a[2,2]-3      b[3,2] <- a[1,1]*(a[1,2]+a[2,2])      if(a[1,2] == 0){          warning("a[1, 2] is zero, using zero for division result b[3,3].")          b[3,3] <- 0      }else if(a[1,1]/a[1,2] < 0){          warning("a[1,1]/a[1,2] is negative, using zero for its square root b[3,3].")          b[3,3] <- 0      }else{          b[3,3] <- sqrt(a[1,1]/a[1,2])      }      b } set.seed(2) a <- matrix(rnorm(4),ncol = 2) fun(a) > > Cheers, > B > > > > > -- > View this message in context: http://r.789695.n4.nabble.com/specific-matrix-element-tranformation-tp4640550p4640554.html> Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > [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. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: specific matrix element tranformation

 In reply to this post by bantex On Aug 16, 2012, at 8:39 PM, bantex wrote: > Hi guys, > > After a long while I came up with this : > > set.seed(2) > a<-matrix(rnorm(4),ncol=2) > abc<-function(a) > { > b=matrix(NA,nrow=3,ncol=3) > b[1,1]=a[1,1]+1 > b[1,2]=a[2,1]*a[2,2] > b[1,3]=a[2,2]+a[1,1] > b[2,1]=a[1,1]-5 > b[2,2]=sqrt(a[2,2]) > b[2,3]=a[1,1]/a[2,2] > b[3,1]=a[2,2]-3 > b[3,2]=a[1,1]*(a[1,2]+a[2,2]) > b[3,3]=sqrt(a[1,1])/a[1,2] > > # return(b=matrix(c(b[1,1],b[1,2],b[1,3],b[2,1],b[2,2],b[2,3], > # b[3,1],b[3,2],b[3,3]),ncol=3))   return(b) > } > > How can I improve on it? > > Cheers, > B > > > > > -- > View this message in context: http://r.789695.n4.nabble.com/specific-matrix-element-tranformation-tp4640550p4640554.html> Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > [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. David Winsemius, MD Alameda, CA, USA ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: specific matrix element tranformation

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## Re: specific matrix element tranformation

 In reply to this post by David Winsemius Thanks David. I have actually 1 more question. How do I assign a name to the output created by this function? Cheers, B
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## Re: specific matrix element tranformation

 On Aug 17, 2012, at 6:04 PM, bantex wrote: > Thanks David. I have actually 1 more question. How do I assign a   > name to the > output created by this function? > abc_ret <- abc(...) > -- > View this message in context: http://r.789695.n4.nabble.com/specific-matrix-element-tranformation-tp4640550p4640680.html> Sent from the R help mailing list archive at Nabble.com. Rhelp is a mailing list. It is NOT Nabble. You are asked in the   Posting Guide to include context. >  >>>>>>>>>>>>>>>> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html >>>>>>>>>>>>>>> David Winsemius, MD Alameda, CA, USA ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.