R help - Sep 2008 - how to pass additional parameters to a function called in tapply?

Hi all,

the following problem is still beyond my R-knowledge:

I have one data vector containing the signal from 4 channels that are measured 
subsequently and in repeating cycles (with one factor vector for cycle and 
one for channel identification).

To extract the mean of each channel during each cycle tapply is the method of 
choice. However, I cannot use the whole measuring period for each channel as 
marked in the factor vector since the hardware switching between channels 
causes some transients in the signal which should not be included when 
calculating the mean.


Instead of using "mean" as function within tapply, I used the
following set of
functions:


start_end.f <- function(x) { c(length(x)*(1-part),length(x)) }


to define the part of the data to use (e.g. part=0.5 the last 50% of the total 
period),

#(part has so far been set universally once for the whole analysis, but see 
below)#


avg.f <- function(x) {
  range <- start_end.f(x)
  mean(x[range[1]:range[2]])
}


and then


tapply(data,factor-vectors,avg.f)


to extract the mean of a subsample of the total measuring period of each 
channel.


The problem now is that I have several signals and different 'parts'
should be
analysed for each, so functions have to be changed to

start_end.f <- function(x,part) { ... }

avg.f <- function(x,part)
  range <- start_end.f(x,part)
  mean(x[range[1]:range[2]])
}


However, this causes an error


Error in FUN(X[[1L]], ...) : argument "part" is missing, with no
default <-


since tapply seems to be unable to pass more than x to the function called



Is there a way to pass variables to the function called in tapply other than 
the dataset extracted by tapply?



Thanks for any help

Wolfgang

try:

tapply(data,factor-vectors,avg.f, part)

On Mon, Sep 1, 2008 at 1:41 PM, Wolfgang Waser <wolfgang.waser at utu.fi>
wrote:
> Hi all,
>
> the following problem is still beyond my R-knowledge:
>
> I have one data vector containing the signal from 4 channels that are
measured
> subsequently and in repeating cycles (with one factor vector for cycle and
> one for channel identification).
>
> To extract the mean of each channel during each cycle tapply is the method
of
> choice. However, I cannot use the whole measuring period for each channel
as
> marked in the factor vector since the hardware switching between channels
> causes some transients in the signal which should not be included when
> calculating the mean.
>
>
> Instead of using "mean" as function within tapply, I used the
following set of
> functions:
>
>
> start_end.f <- function(x) { c(length(x)*(1-part),length(x)) }
>
>
> to define the part of the data to use (e.g. part=0.5 the last 50% of the
total
> period),
>
> #(part has so far been set universally once for the whole analysis, but see
> below)#
>
>
> avg.f <- function(x) {
>  range <- start_end.f(x)
>  mean(x[range[1]:range[2]])
> }
>
>
> and then
>
>
> tapply(data,factor-vectors,avg.f)
>
>
> to extract the mean of a subsample of the total measuring period of each
> channel.
>
>
> The problem now is that I have several signals and different
'parts' should be
> analysed for each, so functions have to be changed to
>
> start_end.f <- function(x,part) { ... }
>
> avg.f <- function(x,part)
>  range <- start_end.f(x,part)
>  mean(x[range[1]:range[2]])
> }
>
>
> However, this causes an error
>
>
> Error in FUN(X[[1L]], ...) : argument "part" is missing, with no
default <-
>
>
> since tapply seems to be unable to pass more than x to the function called
>
>
>
> Is there a way to pass variables to the function called in tapply other
than
> the dataset extracted by tapply?
>
>
>
> Thanks for any help
>
> Wolfgang
>
> ______________________________________________
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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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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