[R] Indexing to Insert values from a dataframe into a matrix

[Daisy Englert Duursma]

Thanks, that worked like a charm.

Daisy

On Wed, Jun 29, 2011 at 11:47 AM, David Winsemius
<dwinsemius at comcast.net> wrote:
>
> On Jun 28, 2011, at 9:18 PM, Daisy Englert Duursma wrote:
>
>> Hello,
>>
>> I think this is a simple problem but I am not coming up with a simple
>> solution. I think it just an indexing problem.
>>
>> I can easily replace values in a matrix from a dataframe when the
>> dataframe has row and column numbers. In the example below I use row
>> and column names and  I can not get it to work
>>
>> #make a matrix where rows and columns are the lat and long for a
>> bounding box of Australia and all elements have the value of -9990
>>
>> bb<-matrix(c(rep(-9999,691*886)),nrow=691
>> ,ncol
>> =886,dimnames=list(seq(-10,-44.50,by=-0.05),seq(112,156.25,by=0.05)))
>>
>> #dfr with row names and col names and values to be replaced in the matrix
>>
>> dfr <- data.frame(cbind(x=seq(120,125,by=0.05), y=-25, var.1=1))
>>
>> #insert the values from the dfr into the matrix
>> bb[dfr$x,dfr$y]<-d$var.1
>
> Indexing with a two column matrix is possible, but those vectors are not
> legitimate indices even if you bundle them into a two column matrix.
> (dfr$y's are all -25, so at least the error report is informative).
>
> These will return indices:
> sapply(as.character(dfr$y), function(x) which(x== dimnames(bb)[[1]]))
> sapply(as.character(dfr$x), function(x) which(x== dimnames(bb)[[2]]))
>
> So try:
>> #insert the values from the dfr into the matrix
>> bb[matrix(c(sapply(as.character(dfr$y), function(x) which(x==
>> dimnames(bb)[[1]])),  sapply(as.character(dfr$x), function(x) which(x==
>> dimnames(bb)[[2]]))), ncol=2)] <- dfr[["var.1"]]
>
>
>>
>> Thanks for your help,
>> Daisy
>>
>> ______________________________________________
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>> 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.
>
> David Winsemius, MD
> West Hartford, CT
>
>



--
Daisy Englert Duursma
Department of Biological Sciences
Room E8C156
Macquarie University, North Ryde, NSW 2109
Australia

Tel +61 2 9850 9256