[R] Calculate Mean of Column Vectors?

[Henrik Bengtsson]

See ?apply. Example

y <- rnorm(3000), dim(y) <- c(3, 1000)
my <- apply(y, MARGIN=2, FUN=mean, na.rm=TRUE) 

to calculate the mean over the 2nd index, that is, for each column, and pass
argument na.rm=TRUE to each call to mean(). This is in practice the same as

my <- rep(NA, ncol(y))
for (kk in 1:ncol(y)) my[kk] <- mean(y[,kk], na.rm=TRUE)

but apply() is to prefer when you get used to it.

Best wishes

Henrik Bengtsson

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Thomas Hopper
> Sent: Tuesday, January 11, 2005 4:46 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Calculate Mean of Column Vectors?
> 
> 
> 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
> 
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