[R] slow access to matrix dimnames

From: Dan Dube <ddube_at_advisen.com>
Date: Fri, 4 Jan 2008 14:29:09 -0500


hello,

i have been trying to convert my data frames to matrices in the hopes of speeding up some of my more complicated scripts.

to assist with this, i am trying to create a "matrix column operator" like $:
"%$%" = function(data,field) {

        as.numeric(data[,grep(field,unlist(dimnames(data)[2]))]) }

the idea here is that you can use a matrix like a dataframe: matrix%$%"fieldname"

i am getting this matrix by converting a dataframe: df = read.csv("data.csv")
matrix = data.matrix(df,rownames.force=FALSE)

this sets rownames to "NULL", but there is still an entry at dimnames(matrix)[1], and so i have to access the actual column names as dimnames(matrix)[2]. if there were only one dimension of dimnames, this operator works quickly, but when i have to access [2], it is super slow.

am i way off base trying to do this? i'd like to have the ability to talk about the columns by name, since they may not always be in the same place. maybe i am making it more complicated than necessary?

thanks!

dan



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