Thanks for the suggestion and the explanation for why I was running into
these troubles.

I've tried:

as.numeric(as.matrix(sample.data[-1, -1]))

However, this creates another vector rather than a matrix.  Is there a
straight forward way to convert this directly into a numeric matrix rather
than a vector?

Additionally, I've also considered:

data.matrix(sample.data[-1,-1]

but bizarrely, it returns:

  x y z
2 1 1 1
3 2 2 2
4 3 3 3

Thanks,
Andrew


On 5/16/07, Marc Schwartz <marc_schwartz@comcast.net> wrote:
>
> On Wed, 2007-05-16 at 08:10 -0400, Andrew Yee wrote:
> > I have the following csv file:
> >
> > name,x,y,z
> > category,delta,gamma,epsilon
> > a,1,2,3
> > b,4,5,6
> > c,7,8,9
> >
> > I'd like to create a numeric matrix of just the numbers in this csv
> dataset.
> >
> > I've tried the following program:
> >
> > sample.data <- read.csv("sample.csv")
> > numerical.data <- as.matrix(sample.data[-1,-1])
> >
> > However, print(numerical.data) returns what appears to be a matrix of
> > characters:
> >
> >   x   y   z
> > 2 "1" "2" "3"
> > 3 "4" "5" "6"
> > 4 "7" "8" "9"
> >
> > How do I force it to be numbers rather than characters?
> >
> > Thanks,
> > Andrew
>
> The problem is that you have two rows which contain alpha entries.
>
> The first row is treated as the header, but the second row is treated as
> actual data, thus overriding the numeric values in the subsequent rows.
>
> You could use:
>
>   as.numeric(as.matrix(sample.data[-1, -1]))
>
> to coerce the matrix to numeric, or if you don't need the alpha entries,
> you could modify the read.csv() call to something like:
>
>   read.csv("sample.csv", header = FALSE, skip = 2, row.names = 1,
>            col.names = c("name", "x", "y", "z")
>
> This will skip the first two rows, set the first column to the row names
> and give you a data frame with numeric columns, which in most cases can
> be treated as a numeric matrix and/or you could explicitly coerce it to
> one.
>
> HTH,
>
> Marc Schwartz
>
>
>

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