[R] HELP: How to subtract a vector out of each row of a matrix or array

[Nordlund, Dan (DSHS/RDA)]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Geoffrey Zhu
> Sent: Thursday, November 15, 2007 10:45 AM
> To: r-help at r-project.org
> Subject: [R] HELP: How to subtract a vector out of each row 
> of a matrix or array
> 
> Hi All,
> 
> I am having great trouble doing something pretty simple.
> 
>  Here is what I did:
> 
> > x <- read.table("clipboard")
> > dim (x)
> [1] 126 10
> > typeof(x)
> [1] "list"
> 
> > w <- array(x)
> > typeof(w)
> "list"
> 
> Q1: How come after constructing an array out of the list, the type of
> the array is still "list"?
> 
> 
> > w <- as.array(x)
> 
> Error in `dimnames<-.data.frame`(`*tmp*`, value = 
> list(c("V1", "V2", "V3",  :
>   invalid 'dimnames' given for data frame
> 
> Q2: How do I covnert a two dimensional list to an array then?
> 
> > y<-as.matrix(x)
> > dim(y)
> [1] 126 10
> 
> Finally, this works.
> 
> > m<-colMeans(y)
> > m
>          V1          V2          V3          V4          V5   
>        V6
> 0.098965679 0.075252330 0.046776996 0.021706852 0.005319685 
> 0.003453889
>          V7          V8          V9         V10
> 0.037819506 0.021107303 0.039035427 0.002694224
> 
> Get the mean of each column.
> 
> Q3: Now the big question. I want to substract V1 from each element of
> column 1, V2 from each element of column 2, ... How do I do this?
> 
> I ended up doing this, which is highly inefficient.
> 
> > z<- t(t(y)-m)
> 
Geoffrey,

How about

   x <- apply(y,1,'-',m)

Hope this is helpful,

Dan

Daniel J. Nordlund
Research and Data Analysis
Washington State Department of Social and Health Services
Olympia, WA  98504-5204