R help - Mar 2006 - calcualtign a trailing 12 column mean in a dataframe?

I have a dataframe of 25 columns and 100,000 rows
called ?testdf?.

I wish to build a new dataframe, with 14 columns and
100,000 rows.

I wish the new dataframe to have the ?trailing 12
column? mean.  That is, I want column 1 of the new
dataframe to have soemthing like:

?( mean(testdf[,1:12],na.rm=T)?

What is the best way to accomplish this?

While we wait for others to provide the best way, here's
one way (if I understand your question correctly):

numrows <- 10
x <- rnorm(25 * numrows)
dat <- as.data.frame(matrix(x, nc = 25))
newdat <- as.data.frame(matrix(0, nr = numrows, nc = 14))
for(j in 1:14) newdat[, j] <- rowMeans(dat[, j:(j + 11)], na.rm = TRUE)

Peter Ehlers

r user wrote:
> I have a dataframe of 25 columns and 100,000 rows
> called ?testdf?.
> 
> I wish to build a new dataframe, with 14 columns and
> 100,000 rows.
> 
> I wish the new dataframe to have the ?trailing 12
> column? mean.  That is, I want column 1 of the new
> dataframe to have soemthing like:
> 
> ?( mean(testdf[,1:12],na.rm=T)?
> 
> What is the best way to accomplish this?
> 
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