Re: [R] Calculate Mean of Column Vectors?

From: Marc Schwartz <MSchwartz_at_medanalytics.com>
Date: Tue 11 Jan 2005 - 15:03:36 EST

On Mon, 2005-01-10 at 22:45 -0500, Thomas Hopper wrote:
> Hello,
>
> I've got an array defined as y <- rnorm(3000), dim(y) <- c(3, 1000).
>
> I'd like to produce a 1000-element vector z that is the mean of the
> corresponding elements of y (like z[1,1] <- mean(y[1,1], y[2,1],
> y[3,1])), but being new to R, I'm not sure how to do this for all
> elements at once (or, at least, simply). Any help is appreciated.
>
> Thanks,
>
> Tom

# You can create 'y' in one step here
y <- matrix(rnorm(3000), ncol = 1000)

# get the column means
z <- colMeans(y)

> str(z)

 num [1:1000] -0.5664 0.8232 -0.0138 -0.5511 1.0224 ...

See ?colMeans for more info.

HTH, Marc Schwartz



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