[R] Calculating a mean based on a factor range

[Peter Alspach]

Tena koe Sam

You could use cut() to convert the depths into your categories and then tapply().

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Sam Albers
> Sent: Friday, 10 June 2011 10:10 a.m.
> To: r-help at r-project.org
> Subject: [R] Calculating a mean based on a factor range
> 
> Hello all,
> 
> I have been using an instrument that collects a temperature profile of
> a
> water column. The instrument records the temperature and depth any time
> it
> takes a reading. I was sampling many times at discrete depth rather
> than a
> complete profile of the water column (e.g. interested in 5m, 10m and
> 20m
> depth position only). The issue was that these measurement were taken
> with
> the instrument hanging off the side of a boat so a big enough wave
> moved the
> instrument such that it recorded a slightly different depth. For my
> purposes, however, this difference is negligible and I wish to consider
> all
> those different readings at close depth as a single depth. So for
> example:
> 
> 
> > library(ggplot2)
> >
> > eg <- read.csv("http://dl.dropbox.com/u/1574243/example_data.csv",
> header=TRUE, sep=",")
> >
> ## Calculating an average value from all the readings for each depth
> reading
> > eg.avg <- ddply(eg, c("site", "depth"), function(df)
> return(c(temp=mean(df$temperature),
> +
> num_samp=length(df$temperature)
> +                                                          )))
> >
> ## An example of my problem
> > eg.avg[eg.avg$num_samp>10 & eg.avg=="Station 3",]
>          site    depth     temp num_samp
> 154 Station 3  1.09000 4.073667       30
> 159 Station 3  2.49744 3.950972       72
> 175 Station 3  7.96332 3.903188       69
> 208 Station 3 19.37708 4.066393       61
> 209 Station 3 19.54096 4.025385       13
> 
> ## So here you will notice that record 208 and 209, by my criteria,
> should
> be considered a sample at the same depth and lumped together. Yet I
> can't
> figure out a way to coerce R to calculate a mean value of temperature
> based
> on a threshold range depth (say +/- 0.25). Generally speaking this can
> be
> said to be calculating a mean (temperature) based on a factor (depth)
> range.
> 
> Any thoughts on this? I am using R 2.12.1.
> 
> Thanks in advance!
> 
> Sam
> 
> 	[[alternative HTML version deleted]]
> 
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