Excellent! I completely forgot its name and existence. Perhaps ave
should be mentioned on the help page of either by, tapply, split.
Many thanks,
baptiste
On 10 Dec 2008, at 17:20, Chuck Cleland wrote:
On 12/10/2008 12:02 PM, baptiste auguie wrote:
Dear list,
I have a data.frame with x, y values and a 3-level factor "group",
say.
I want to create a new column in this data.frame with the values of y
scaled to 1 by group. Perhaps the example below describes it best:
x <- seq(0, 10, len=100)
my.df <- data.frame(x = rep(x, 3), y=c(3*sin(x), 2*cos(x),
cos(2*x)),
# note how the y values have a different maximum depending on the
group
group = factor(rep(c("sin", "cos", "cos2"), each=100)))
library(reshape)
df.melt <- melt(my.df, id=c("x","group")) # make a long format
df.melt <- df.melt[ order(df.melt$group) ,] # order the data.frame
by
the group factor
df.melt$norm <- do.call(c, tapply(df.melt$value, df.melt$group,
function(.v) {.v / max(.v)})) # calculate the normalised value per
group and assign it to a new column
library(lattice)
xyplot(norm + value ~ x,groups=group, data=df.melt, auto.key=T) #
check that it worked
This procedure works, but it feels like I'm reinventing the wheel
using
hammer and saw. I tried to use aggregate, by, ddply (plyr package),
but
I coudn't find anything straight-forward.
with(my.df, ave(y, group, FUN = function(x){x/max(x)}))
?ave
I'll appreciate any input,
Baptiste
_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Chuck Cleland, Ph.D.
NDRI, Inc. (www.ndri.org)
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 512-0171 (M, W, F)
fax: (917) 438-0894
_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
