[R] Sums based on values of other matrix

[arun]

Hi,
If you have missing values:
 set.seed(125)
 A<- matrix(sample(c(NA,0:9),10*10,replace=TRUE),10,10)
 set.seed(49)
 B<- matrix(sample(c(NA,1:25),10*10,replace=TRUE),10,10)
B1<- matrix(0,nrow=nrow(B),ncol=ncol(B))
 B1[A==1 & !is.na(A)]<- B[A==1 & !is.na(A)]
 rowSums(B1)
 #[1]  0  0 38  7 16  0  0  1  6 18


#Speed comparison

set.seed(485)
Anew<- matrix(sample(c(NA,0:9),3e5*70,replace=TRUE),3e5,70)
set.seed(944)
Bnew<- matrix(sample(c(NA,1:25),3e5*70,replace=TRUE),3e5,70)
B2<- Bnew
B3<- matrix(0,nrow=nrow(Bnew),ncol=ncol(Bnew))

system.time({
 B3[Anew==1 & !is.na(Anew)]<- Bnew[Anew==1 & !is.na(Anew)]
res1<- rowSums(B3)
})
# user  system elapsed 
#  2.916   0.308   3.232 

system.time({
vec1<-ifelse(Anew == 1 & !is.na(Anew), B2, 0)
res2<- rowSums(vec1)
})
# user  system elapsed 
#  7.012   0.744   7.775 
 identical(res1,res2)
#[1] TRUE


A.K.



Dear Sarah, 

this works very well! If fulfills what I need, however, there is
 a small performance problem: I have 300.000 rows and 70 columns. With 
missing values. 
Besides that you directly hit the key. 

Thanks, 
Tobias 


----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: tobias schlager <tobebryant at me.com>
Cc: R help <r-help at r-project.org>
Sent: Thursday, September 26, 2013 6:34 PM
Subject: Re: [R] Sums based on values of other matrix

Hi,
Try:
A<- structure(c(1, 2, 1, 2, 2, 1, 2, 1), .Dim = c(2L, 4L))
B<- structure(c(3, 1, 4, 1, 2, 2, 1, 2), .Dim = c(2L, 4L))
 B1<- matrix(0,nrow(B),ncol(B))
B1[A==1]<-B[A==1]
 rowSums(B1)
#[1] 7 4
A.K.




----- Original Message -----
From: tobias schlager <tobebryant at me.com>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Thursday, September 26, 2013 5:51 PM
Subject: [R] Sums based on values of other matrix

Dear all, 

I have a big problem: 
- I got two matrices, A and B 
- A shows identifies the value of B, however the values of B must be summed 
- For instance, 
1 1 2 2 
2 2 1 1 
gives matrix a 
3 4 2 1 
1 1 2 2 
gives matrix b 

Now the result for the value 1 would be 
7 
4 
which are the rowsums of the values of matrix B given that matrix A has the value 1. 


How can I do this automatically? I am really puzzled here. Thanks for your help guys, 
Tobi
    [[alternative HTML version deleted]]

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