[R] help with matrix
jim holtman
jholtman at gmail.com
Mon Dec 31 05:21:14 CET 2007
Does this give you want you want? I assume that you have to also
ignore the first column in matrixC or else you don't have a reasonable
comparison. Also your data for matrixA and matrixB did not have any
spaces between the numbers, so I just took a guess at what they should
be.
> a.m <- scan(textConnection(" 1.851 1.4 0.083 1.001
+ 0.877 1.3 0.116 1.33
+ 1.902 1.2 1.102 0.302
+ 0.864 0.126 1.11 0.252
+ 1.823 0.216 1.002 0.307"))
Read 20 items
> a.m <- matrix(a.m, ncol=4, byrow=TRUE)[, -1] # ignore 1st column
>
> b.m <- scan(textConnection(" 0.876 1.77 0.193 0.328
+ 0.891 1.009 0.238 1.004
+ 0.864 1.115 0.276 0.22
+ 0.887 1.306 0.166 0.239
+ 0.852 1.001 1.008 0.251"))
Read 20 items
> b.m <- matrix(b.m, ncol=4, byrow=TRUE)[, -1]
>
> c.m <- scan(textConnection(" 0.5 1.0 0.5 1.0
+ 1.0 1.0 1.0 0.5
+ 1.0 1.0 1.0 0.5
+ 1.0 1.0 1.0 0.5
+ 0.5 0.5 1.0 0.5"))
Read 20 items
> c.m <- matrix(c.m, ncol=4, byrow=TRUE)[, -1]
> closeAllConnections()
>
> result <- a.m * b.m
> # set to NA entries where c.m != 1
> is.na(result) <- c.m != 1
> result
[,1] [,2] [,3]
[1,] 2.478000 NA 0.328328
[2,] 1.311700 0.027608 NA
[3,] 1.338000 0.304152 NA
[4,] 0.164556 0.184260 NA
[5,] NA 1.010016 NA
>
On Dec 30, 2007 10:52 PM, Yingchen Wang <riddle_chen94 at yahoo.com> wrote:
> Hi, dear all:
> I am a beginner. I appreciate any help or hint from you.
> I am trying to do calculation with matrices. I have 3 matrices. One is matrixA, 2nd is matrixB, and last is matrixC.
> Here is matrixA:
> 1.8511.40.0831.001
> 0.8771.30.1161.33
> 1.9021.21.1020.302
> 0.8640.1261.110.252
> 1.8230.2161.0020.307
>
> Next is matrixB:
> 0.8761.770.1930.328
> 0.8911.0090.2381.004
> 0.8641.1150.2760.22
> 0.8871.3060.1660.239
> 0.8521.0011.0080.251
>
> Last is matrixC:
> 0.5 1.0 0.5 1.0
> 1.0 1.0 1.0 0.5
> 1.0 1.0 1.0 0.5
> 1.0 1.0 1.0 0.5
> 0.5 0.5 1.0 0.5
>
> What I want is to match both matrixA and matrixB with matrixC. Ignore the 1st column in matrixA and matrixB. When the element im matrixC is 1.0, multilply the corresponding element in matrixA by the corresponding element in matrixB. Otherwise, ignore it. I wrote the following code with some error in the logic:
>
>
> A<-read.table('matrixA.txt', header=F)
> B<-read.table('matrixB.txt', header=F)
> C<-read.table('matrixC.txt', header=F)
> a1<-as.matrix(A[,1])
> arest<-as.matrix(A[,2:5])
> b1<-as.matrix(B[,1])
> brest<-as.matrix(B[,2:5])
> C<-as.matrix(C)
> if(C= =1){
> ra<-(arest*brest)
> }else {
> throw<-(arest*brest)
> }
> ra
>
> I got a warning message:
> Warning message:the condition has length > 1 and only the first element will be used in: if.....
>
> When I changed the if part to:
> ifelse (C= =1,ra<-(arest*brest),throw<-(arest*brest))
>
> The result is the multiplication of each element in matrixA and matrixB.
>
> Anyone has an idea about what is wrong. Thanks
>
> Riddle
>
>
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--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
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