[R] group means
Henrik Bengtsson
hb at maths.lth.se
Fri Feb 21 00:33:03 CET 2003
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
Office: Bioinformatics, WEHI, Parkville
+61 (0)412 269 734 (cell), +61 (0)3 9345 2324 (lab),
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hb at wehi.edu.au, http://www.maths.lth.se/~hb/
Time zone: +11h UTC (Sweden +1h UTC, Calif. -8h UTC)
> -----Original Message-----
> From: r-help-admin at stat.math.ethz.ch
> [mailto:r-help-admin at stat.math.ethz.ch] On Behalf Of Jeremy Z Butler
> Sent: den 21 februari 2003 09:44
> To: r-help at stat.math.ethz.ch
> 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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