R help - Apr 2013 - Using different function (parameters) with apply

Hi All,

I have the following problem (read the commented bit below):

a<-matrix(1:9,nrow=3)


a

     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9


div<-1:3

apply(a,2,function(x)x/div) ##want to divide each column by div-
instead each row is divided##


     [,1] [,2] [,3]
[1,]    1  4.0    7
[2,]    1  2.5    4
[3,]    1  2.0    3


apply(a,1,function(x)x/div) ##Changing Margin from 2 to 1 does
something completele weird##         [,1]     [,2] [,3]
[1,] 1.000000 2.000000    3
[2,] 2.000000 2.500000    3
[3,] 2.333333 2.666667    3


Any thoughts?


Thanks,

Sachin

	[[alternative HTML version deleted]]

Hi.

It would be easier to help you if you show us the result you are trying to
obtain.

Here are my attempts:
> sweep(a,2,div, FUN="/")
     [,1] [,2]     [,3]
[1,]    1  2.0 2.333333
[2,]    2  2.5 2.666667
[3,]    3  3.0 3.000000

or
> a/matrix(rep(div,3),ncol=3, byrow=TRUE)
     [,1] [,2]     [,3]
[1,]    1  2.0 2.333333
[2,]    2  2.5 2.666667
[3,]    3  3.0 3.000000

Hope this helps.

Andrija




On Thu, Apr 18, 2013 at 7:20 AM, Sachinthaka Abeywardana <
sachin.abeywardana@gmail.com> wrote:
> Hi All,
>
> I have the following problem (read the commented bit below):
>
> a<-matrix(1:9,nrow=3)
>
>
> a
>
>      [,1] [,2] [,3]
> [1,]    1    4    7
> [2,]    2    5    8
> [3,]    3    6    9
>
>
> div<-1:3
>
> apply(a,2,function(x)x/div) ##want to divide each column by div-
> instead each row is divided##
>
>
>      [,1] [,2] [,3]
> [1,]    1  4.0    7
> [2,]    1  2.5    4
> [3,]    1  2.0    3
>
>
> apply(a,1,function(x)x/div) ##Changing Margin from 2 to 1 does
> something completele weird##         [,1]     [,2] [,3]
> [1,] 1.000000 2.000000    3
> [2,] 2.000000 2.500000    3
> [3,] 2.333333 2.666667    3
>
>
> Any thoughts?
>
>
> Thanks,
>
> Sachin
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org 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.
>
	[[alternative HTML version deleted]]

On 18-04-2013, at 07:20, Sachinthaka Abeywardana <sachin.abeywardana at
gmail.com> wrote:
> Hi All,
> 
> I have the following problem (read the commented bit below):
> 
> a<-matrix(1:9,nrow=3)
> 
> 
> a
> 
>     [,1] [,2] [,3]
> [1,]    1    4    7
> [2,]    2    5    8
> [3,]    3    6    9
> 
> 
> div<-1:3
> 
> apply(a,2,function(x)x/div) ##want to divide each column by div-
> instead each row is divided##
> 
> 
>     [,1] [,2] [,3]
> [1,]    1  4.0    7
> [2,]    1  2.5    4
> [3,]    1  2.0    3
> 
column 1 is c(1,2,3) and divided by your vector div gives the first column
c(1/1,2/2,3/3) = c(1,1,1) and that is correct.
column 3 is c(7,8,9) and divided by vector div gives c(7/1, 8/2 , 9/3) =
c(7,4,3). Also correct.

> apply(a,1,function(x)x/div) ##Changing Margin from 2 to 1 does
> something completele weird##         [,1]     [,2] [,3]
> [1,] 1.000000 2.000000    3
> [2,] 2.000000 2.500000    3
> [3,] 2.333333 2.666667    3
> 
You are dividing each row by vector div). The result for row 1 is the first
column and so forth.
Probably if you did t(?) you would get what you want/expect.
> Any thoughts?
> 
Your conclusions are incorrect.
What is the result that you want (or expect)?

Berend

On Apr 17, 2013, at 10:20 PM, Sachinthaka Abeywardana wrote:
> Hi All,
> 
> I have the following problem (read the commented bit below):
> 
> a<-matrix(1:9,nrow=3)
> 
> 
> a
> 
>     [,1] [,2] [,3]
> [1,]    1    4    7
> [2,]    2    5    8
> [3,]    3    6    9
> 
> 
> div<-1:3
> 
> apply(a,2,function(x)x/div) ##want to divide each column by div-
> instead each row is divided##
No. Each column is divided by that vector 'div'. Try:

1:3/1:3
4:6/1:3
7:9/1:3
>     [,1] [,2] [,3]
> [1,]    1  4.0    7
> [2,]    1  2.5    4
> [3,]    1  2.0    3
> 
> 
> apply(a,1,function(x)x/div) ##Changing Margin from 2 to 1 does
> something completele weird##         [,1]     [,2] [,3]
> [1,] 1.000000 2.000000    3
> [2,] 2.000000 2.500000    3
> [3,] 2.333333 2.666667    3
Each row is divided by that vector but then returned as columns. Try it with a
matrix that has a different number of columns than rows.

-- 

David Winsemius
Alameda, CA, USA