How about:
> group.means <- function(x, k=5){
+ n.gps <- floor(length(x)/k)
+ rep(1, k) %*% array(x[1:(k*n.gps)], dim=c(k, n.gps))
+ }
> group.means(c(3.4, 6.0, 2.5, 7.5, 1.8, 4.2, 6.4, 5.7, 17.2, 13.5))
[,1] [,2]
[1,] 21.2 47
Best Wishes,
Spencer Graves
Henrik Bengtsson wrote:
When all groups have the same number of elements and the groups are
consecutive I normally transform the vector into a matrix where each
column contains data from one group. Then I perform whatever on each
group using apply():
x <- c(3.4, 6.0, 2.5, 7.5, 1.8, 4.2, 6.4, 5.7, 17.2, 13.5)
xm <- matrix(x, nrow=5) # matrix() "fills by column" by default
print(xm)
# [,1] [,2]
# [1,] 3.4 4.2
# [2,] 6.0 6.4
# [3,] 2.5 5.7
# [4,] 7.5 17.2
# [5,] 1.8 13.5
m <- apply(xm, MARGIN=2, FUN=mean, na.rm=TRUE) # MARGIN=2 means "along
columns" or "columnwise"
print(m)
# [1] 4.24 9.40
Hope this helps
Henrik Bengtsson
Home: 201/445 Royal Parade, 3052 Parkville
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+61 (0)412 269 734 (cell), +61 (0)3 9345 2324 (lab),
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Time zone: +11h UTC (Sweden +1h UTC, Calif. -8h UTC)
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]] On Behalf Of Jeremy Z Butler
Sent: den 21 februari 2003 09:44
To: [EMAIL PROTECTED]
Subject: [R] group means
Hi,
Any hints on how I would generate the means of each 5 number
group in a
column of numbers in data.frame form. i.e. get mean of first
five in column
and then mean of second five in column etc. etc.
1 3.4
2 6.0
3 2.5
4 7.5
5 1.8
6 4.2
7 6.4
8 5.7
9 17.2
10 13.5
Grateful for any suggestions
Jeremy
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