R help - Feb 2004 - Apply a function to each cell of a ragged matrix

R-Helpers:

There are a matrix x and a factor f.  nrow(x) == length(f), e.g.:
x <- matrix(1:6, nrow = 3)
f <- factor(c("daytime", "daytime", "night"))

I want the sum of all elements of rows of "x" for each corresponding
level in factor "f",
In this case, I want output like:
"daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
"night"   [2] x[3,1]+x[3,2]

But, tapply(x,f,sum) or by(x,f,sum) do not work.  What other functions can I
use?

Thank you very much

Xiao

> sapply(split(x,f), sum)
daytime   night 
     12       9 

HTH,
Andy
> From: XIAO LIU
> 
> R-Helpers:
> 
> There are a matrix x and a factor f.  nrow(x) == length(f), e.g.:
> x <- matrix(1:6, nrow = 3)
> f <- factor(c("daytime", "daytime",
"night"))
> 
> I want the sum of all elements of rows of "x" for each 
> corresponding level in factor "f",
> In this case, I want output like:
> "daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
> "night"   [2] x[3,1]+x[3,2]
> 
> But, tapply(x,f,sum) or by(x,f,sum) do not work.  What other 
> functions can I use?
> 
> Thank you very much
> 
> Xiao

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rowsum(x,f)

---
Date:   Tue, 17 Feb 2004 17:38:46 -0500 
From:   XIAO LIU <xiaoliu at jhmi.edu>
To:   R Help <r-help at stat.math.ethz.ch> 
Subject:   [R] Apply a function to each cell of a ragged matrix 

 
R-Helpers:

There are a matrix x and a factor f. nrow(x) == length(f), e.g.:
x <- matrix(1:6, nrow = 3)
f <- factor(c("daytime", "daytime", "night"))

I want the sum of all elements of rows of "x" for each corresponding
level in factor "f",
In this case, I want output like:
"daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
"night" [2] x[3,1]+x[3,2]

But, tapply(x,f,sum) or by(x,f,sum) do not work. What other functions can I use?

Thank you very much

Xiao

Hi,
you could simply use functions such as:

time <- dim (3)
for ( i in 1:3) time [i] <- x[i,1]+x[i,2]

the result of time will be the sum of rows.

best regards..

----- Original Message -----
From: "XIAO LIU" <xiaoliu at jhmi.edu>
To: "R Help" <r-help at stat.math.ethz.ch>
Sent: Wednesday, February 18, 2004 12:38 AM
Subject: [R] Apply a function to each cell of a ragged matrix

> R-Helpers:
>
> There are a matrix x and a factor f.  nrow(x) == length(f), e.g.:
> x <- matrix(1:6, nrow = 3)
> f <- factor(c("daytime", "daytime",
"night"))
>
> I want the sum of all elements of rows of "x" for each
corresponding level
in factor "f",
> In this case, I want output like:
> "daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
> "night"   [2] x[3,1]+x[3,2]
>
> But, tapply(x,f,sum) or by(x,f,sum) do not work.  What other functions can
I use?
>
> Thank you very much
>
> Xiao
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>
>

I misread your post.  Try any of these:

rowSums(rowsum(x,f))

rowsum(rowSums(x),f)

tapply(rowSums(x),f,sum)

by(rowSums(x),f,sum)

---

Date:   Tue, 17 Feb 2004 19:10:11 -0500 (EST) 
From:   Gabor Grothendieck <ggrothendieck at myway.com>
To:   <xiaoliu at jhmi.edu>, <r-help at stat.math.ethz.ch> 
Subject:   RE: [R] Apply a function to each cell of a ragged matrix 

 


rowsum(x,f)

---
Date: Tue, 17 Feb 2004 17:38:46 -0500 
From: XIAO LIU <xiaoliu at jhmi.edu>
To: R Help <r-help at stat.math.ethz.ch> 
Subject: [R] Apply a function to each cell of a ragged matrix 


R-Helpers:

There are a matrix x and a factor f. nrow(x) == length(f), e.g.:
x <- matrix(1:6, nrow = 3)
f <- factor(c("daytime", "daytime", "night"))

I want the sum of all elements of rows of "x" for each corresponding
level in factor "f",
In this case, I want output like:
"daytime" [1] x[1,1]+x[2,1]+x[1,2]+x[2,2]
"night" [2] x[3,1]+x[3,2]

But, tapply(x,f,sum) or by(x,f,sum) do not work. What other functions can I use?