peter leonard
2003-May-31 15:35 UTC
[R] function to populate a matrix based on a lookup to another matrix ?
Hi,
This is a beginner R question.
I have a 4x4 matrix named 'lookup' with the following values:
1 2 3 4
1 0.000000 2.828427 5.656854 8.485281
2 2.828427 0.000000 2.828427 5.656854
3 5.656854 2.828427 0.000000 2.828427
4 8.485281 5.656854 2.828427 0.000000
I then create a new empty matrix named 'dd' with specfic row and col
names :
1 3 4 3 3 1
1 NA NA NA NA NA NA
2 NA NA NA NA NA NA
3 NA NA NA NA NA NA
4 NA NA NA NA NA NA
3 NA NA NA NA NA NA
2 NA NA NA NA NA NA
1 NA NA NA NA NA NA
I want to be able populate the cells in 'dd' using 'lookup'
based on the
specified rownames and colnames of 'dd'. For example, the cell in
'dd' where
the rowname =2 and the colname = 1 should be assigned the value 2.828427 .
I've tried several ways of doing this with the apply function but without
success. I can do it with a for loop but I want to avoid that for efficiency
reasons.
After running the function, as an example, the first column of 'dd'
should
look like this :
1
1 0.000000000
2 2.828427125
3 5.656854249
4 8.485281374
3 5.656854249
2 2.828427125
1 0.000000000
Can anyone please help me identify the required function or an alternative
way of achieving the same result? Hopefully this is simple and I'm just not
seeing it.
Thanks
Peter
Uwe Ligges
2003-May-31 15:58 UTC
[R] function to populate a matrix based on a lookup to another matrix ?
peter leonard wrote:> Hi, > > This is a beginner R question. > > I have a 4x4 matrix named 'lookup' with the following values: > > 1 2 3 4 > 1 0.000000 2.828427 5.656854 8.485281 > 2 2.828427 0.000000 2.828427 5.656854 > 3 5.656854 2.828427 0.000000 2.828427 > 4 8.485281 5.656854 2.828427 0.000000 > > I then create a new empty matrix named 'dd' with specfic row and col > names : > > 1 3 4 3 3 1 > 1 NA NA NA NA NA NA > 2 NA NA NA NA NA NA > 3 NA NA NA NA NA NA > 4 NA NA NA NA NA NA > 3 NA NA NA NA NA NA > 2 NA NA NA NA NA NA > 1 NA NA NA NA NA NA > > I want to be able populate the cells in 'dd' using 'lookup' based on the > specified rownames and colnames of 'dd'. For example, the cell in 'dd' > where the rowname =2 and the colname = 1 should be assigned the value > 2.828427 . > > I've tried several ways of doing this with the apply function but > without success. I can do it with a for loop but I want to avoid that > for efficiency reasons. > > After running the function, as an example, the first column of 'dd' > should look like this : > > 1 > 1 0.000000000 > 2 2.828427125 > 3 5.656854249 > 4 8.485281374 > 3 5.656854249 > 2 2.828427125 > 1 0.000000000 > > Can anyone please help me identify the required function or an > alternative way of achieving the same result? Hopefully this is simple > and I'm just not seeing it. > > Thanks > Peter >dd <- lookup[as.numeric(rownames(dd)), as.numeric(colnames(dd))] and after that restoring dd's row- and colnames. Anyway, I guess you don't need to create "dd". Just calculate those rownames (rn) and colnames (cn) as integers. Then the following works: dd <- lookup[rn, cn] Uwe Ligges
Gabor Grothendieck
2003-May-31 23:38 UTC
[R] function to populate a matrix based on a lookup to another matrix ?
peter leonard wrote:> I have a 4x4 matrix named 'lookup' with the following values:[...]> I then create a new empty matrix named 'dd' with specfic row and col > names : > > 1 3 4 3 3 1 > 1 NA NA NA NA NA NA > 2 NA NA NA NA NA NA > 3 NA NA NA NA NA NA > 4 NA NA NA NA NA NA > 3 NA NA NA NA NA NA > 2 NA NA NA NA NA NA > 1 NA NA NA NA NA NA > > I want to be able populate the cells in 'dd' using 'lookup' based on the > specified rownames and colnames of 'dd'. For example, the cell in 'dd'If an R matrix is subscripted by an n by 2 matrix of row,column index pairs then the result is a vector of length n with the corresponding values taken from that matrix. Thus, suppose: rn <- c(1:4,3:1) cn <- c(1,3,4,3,3,1) Then dd strung out into a vector is: dd.vec <- lookup[as.matrix(expand.grid(rn,cn))] and reshaping this vector into a matrix gives: dd <- matrix(result.vec,nr=length(rn))
peter leonard
2003-Jun-01 00:58 UTC
[R] function to populate a matrix based on a lookup to another matrix ?
That worked perfect. Thanks for the fast response. Peter Leonard>From: Uwe Ligges <ligges at statistik.uni-dortmund.de> >To: peter leonard <pfleonard at hotmail.com> >CC: r-help at stat.math.ethz.ch >Subject: Re: [R] function to populate a matrix based on a lookup to another >matrix ? >Date: Sat, 31 May 2003 17:58:27 +0200 > >peter leonard wrote: >>Hi, >> >>This is a beginner R question. >> >>I have a 4x4 matrix named 'lookup' with the following values: >> >> 1 2 3 4 >>1 0.000000 2.828427 5.656854 8.485281 >>2 2.828427 0.000000 2.828427 5.656854 >>3 5.656854 2.828427 0.000000 2.828427 >>4 8.485281 5.656854 2.828427 0.000000 >> >>I then create a new empty matrix named 'dd' with specfic row and col names >>: >> >> 1 3 4 3 3 1 >>1 NA NA NA NA NA NA >>2 NA NA NA NA NA NA >>3 NA NA NA NA NA NA >>4 NA NA NA NA NA NA >>3 NA NA NA NA NA NA >>2 NA NA NA NA NA NA >>1 NA NA NA NA NA NA >> >>I want to be able populate the cells in 'dd' using 'lookup' based on the >>specified rownames and colnames of 'dd'. For example, the cell in 'dd' >>where the rowname =2 and the colname = 1 should be assigned the value >>2.828427 . >> >>I've tried several ways of doing this with the apply function but without >>success. I can do it with a for loop but I want to avoid that for >>efficiency reasons. >> >>After running the function, as an example, the first column of 'dd' should >>look like this : >> >> 1 >>1 0.000000000 >>2 2.828427125 >>3 5.656854249 >>4 8.485281374 >>3 5.656854249 >>2 2.828427125 >>1 0.000000000 >> >>Can anyone please help me identify the required function or an alternative >>way of achieving the same result? Hopefully this is simple and I'm just >>not seeing it. >> >>Thanks >>Peter >> > > dd <- lookup[as.numeric(rownames(dd)), as.numeric(colnames(dd))] >and after that restoring dd's row- and colnames. > >Anyway, I guess you don't need to create "dd". Just calculate those >rownames (rn) and colnames (cn) as integers. Then the following works: > > dd <- lookup[rn, cn] > >Uwe Ligges >