[R] Average of data files in a directory

[Peter Perez]

Hi,

Thanks to Henrique and Prof. Spector for their kind reply. Indeed, the mean
function does work, but the result I want is an average data vector, not an
scalar, which is the output of mean(). This is, given these two data frames
(each data frame has 500 rows):

Time  Pressure  
0.0     100
1.0     200
2.0     300

And
Time  Pressure  
0.0     200
1.0     300
2.0     400

By computing the average, c = (a+b)/2, I would get:
Time  Pressure  
0.0     150
1.0     250
2.0     350

For a few vectors I could simply use the formula c = (a+b)/2, but I have
about 40 data files for each directory and was looking for an automatic way
to do this. Here is the code I have so far:

listfiles <- list.files(pattern=".pre")    # list all datafiles in
thedirectory
loadfiles <- lapply(listfiles,read.csv)  # read the csv files
meanDataFrame <- lapply(loadfiles, ?????)

Thanks again for your help...

Best regards,
Peter Perez

EMS Energy Institutute
The Pennsylvania State University
University Park, PA 16802



The mean function works in data.frames:

lapply(loadfiles, mean)
[[1]]
    Time Pressure
  1.0000 323.3333

[[2]]
    Time Pressure
  1.0000 323.3333


On Wed, Jul 1, 2009 at 1:50 PM, plpd00 <plpd00 at gmail.com> wrote:

>
> Dear all,
>
> I know it is as simple as c <- (a + b)/2 to compute the average
> (element-wise) of two data vectors. However, I can't work out to compute
> the
> average when you have many data vectors in a directory. I have done this:
> ------------------------------------
> setwd("/.../data/")
> listfiles <- list.files(pattern=".pre")    # list all datafiles in the
> directory
> loadfiles <- lapply(listfiles,read.csv)  # read the csv files
> meanData <- lapply(loadfiles,mean) # intended to compute the element-wise
> average.
> ------------------------------------
> Which does not produce the right result. Let me explain myself better...
> The
> data files have the form (500 rows):
> Time,Pressure
> 0,300
> 1,320
> 2,350
> And I want to compute the average time (which is trivial since all time
> vectors are the same) and the average pressure (from all the data files
> collected). I know the function "mean" is not the one to use, but I cannot
> find any function that allows me to compute average of two vectors. I hope
> this is clear enough for you guys to understand. Thanks in advance for
> your
> kind attention.
>
> Best regards,
> Peter
>
> --
> View this message in context:
> http://www.nabble.com/Average-of-data-files-in-a-directory-tp24293290p24293290.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at 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.
>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

-- 
View this message in context: http://www.nabble.com/Average-of-data-files-in-a-directory-tp24293290p24306925.html
Sent from the R help mailing list archive at Nabble.com.