[R] read.table or read.csv without row index?

[David Winsemius]

On May 5, 2010, at 3:49 PM, JiHO wrote:

>> I tried as.matrix but it did not help.
>
> as.matrix() won't work because a matrix requires everything in it to
> be of the same type (number, character, logical etc.). You do not have
> only numbers in your data.frame, so it will convert everything to
> character strings. If you try as.matrix(temp[,-1]) it should work
> (assuming you only have characters in the first column, otherwise
> remove all non-numeric columns).
>
> But what you really want is to circumvent the fact that, on a
> data.frame, mean works column-wise. In fact, when you call mean() on a
> data.frame() it calls mean.data.frame(), which code you can see by
> typing its name at the prompt:
>
>> mean.data.frame
>    function (x, ...)
>    sapply(x, mean, ...)
>    <environment: namespace:base>
>
> And indeed, it uses sapply() to apply the function mean to each
> column. You could have tried:
>
>    mean.default(temp[2,2:3])
>
> but this returns and error because it needs a numeric vector and does
> not automatically convert your data.frame into it. So you need:
>
>    mean.default(as.numeric(temp[2,2:3]))

Or:

mean( data.matrix(temp)[ 2 , 2:3] )


>
> or more simply
>
>    mean(as.numeric(temp[2,2:3]))
>
> I hope that helped. Sincerely,
>
> JiHO
> ---
> http://maururu.net
>
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David Winsemius, MD
West Hartford, CT