see inline



________________________________
 From: PIKAL Petr <petr.pikal@precheza.cz>

Sent: Wednesday, March 27, 2013 11:24 AM
Subject: RE: [R] Averaging Out many rows from a column AND funtion to string

Hi

> -----Original Message-----
> From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-
> project.org] On Behalf Of Alaios
> Sent: Wednesday, March 27, 2013 9:13 AM
> To: R help
> Subject: [R] Averaging Out many rows from a column AND funtion to
> string
> 
> Dear all,
> 1) I have a very large matrix of
> str(keep)
>  num [1:153899, 1:3415] -98.6 -95.8 -96.4 -95.8 -98 ...
> that  I would like to reduce its size to something like
> 
> str(keep)
>  num [1:1000, 1:3415] -98.6 -95.8 -96.4 -95.8 -98 ... or anything
> similar in size as this is a matrix that needs plotting (so is ok if it
> is 1000 row, 995, or 1123)
> 
> I think what I need here is a way of selecting multiple rows and
> averaging per column (notice that the column number should stay the
> same)

Make an index variable and aggregate values according it

Something like
idx<-cut(1:153899, 153)
keep.ag<-aggregate(keep, list(idx), mean)

1) Thanks that returned a data frame.. How I can have a matrix at the end?
2) I want to have a string that can be used also for calling a function with the same name. Think of using "mean" to call mean. I need to have R interpret the string in different ways.

Regards
Alex

> 
> b. I would like to be able to convert strings that are function names
> to real function calls. For example I have something like
> 
> LogFunction<- function(){}
> FunctionIndex<- rbind (c(1,"LogFunction"),
>                c(2,"TakeFunction")
>               )
> print(sprintf('Using the function %s',FunctionIndex[1,1])) # call the
> FunctionIndex[1,1] somehow

I am not sure if I understand correctly. 

Is this what you want?
myf <-function(fun="mean", arg) eval(call(fun, arg))

Regards
Petr

> 
> 
> 
> I would like to thank you in advance for your help
> 
> Regards
> Alex
> 
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