[R] means by column after split

[S.McClatchie]

Colleagues

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System info:
R version rw1020 on NT
ESS using emacs ver. 20.4

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I need to get the means for each column of a dataframe in the list 
created by splitting a data frame. At present, I am getting the mean of all 
columns in aggregate.

The structure of the unsplit data is:

> shuttle.tr1[1:10,]
      juliandate       lat temp.degC
24892   305.9581 -43.18243  11.90729
24893   305.9581 -43.18258  11.90854
24894   305.9582 -43.18272  11.94356
24895   305.9582 -43.18286  11.95356
24896   305.9583 -43.18300  11.95544
24897   305.9583 -43.18315  11.97670
24898   305.9584 -43.18329  11.99171
24899   305.9584 -43.18343  11.99546
24900   305.9585 -43.18358  11.98546
24901   305.9585 -43.18372  11.98858

Now I split the data into 8 groups:

> fine <- 8
> fsh <- factor(cut(shuttle.tr1$juliandate, fine))
> b.shuttle.tr1 <- split.data.frame(shuttle.tr1, fsh)

Here's where i need help, in getting the mean by columns:

> b.shuttle.tr1 <-  data.frame(sapply(b.shuttle.tr1, mean))
> b.shuttle.tr1
                sapply.b.shuttle.tr1..mean.
(305.96,306.02]                    91.51870
(306.02,306.09]                    91.41042
(306.09,306.16]                    91.12872
(306.16,306.23]                    90.15020
(306.23,306.29]                    89.94670
(306.29,306.36]                    89.91251
(306.36,306.43]                    89.83651
(306.43,306.5]                     90.00933
> 

Help will be appreciated.
Thanks

Sam

Sam McClatchie, Research scientist (fisheries acoustics))))))))))
NIWA (National Institute of Water & Atmospheric Research Ltd)
PO Box 14 901, Kilbirnie, Wellington, New Zealand
s.mcclatchie at niwa.cri.nz 

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