[R] plotting multiple animal tracks against Date/Time

[Gabor Grothendieck]

On Wed, Sep 29, 2010 at 7:52 AM, Struve, Juliane
<j.struve at imperial.ac.uk> wrote:
> I will post the example again to see if its readable now. My question is why
> does read.zoo(file=filenames,....) work and  lapply(filenames, read.zoo,...) does not ? Since I am reading the same file in both statements I just do not know how to interpret "Error in strptime(x, format, tz = tz) : invalid 'x' argument".
>
> Thank you for all help.
>
> Juliane
>
>  library(chron)
>  library(zoo)
>  #Generate example file
>  Fish_ID=1646
>  Date <- "01/01/2004 00:01:00"
>  Date <- as.POSIXct(strptime(Date,format="%m/%d/%Y %H:%M:%S"))
>  R2sqrt <-100
>  Test <- data.frame(Fish_ID=Fish_ID,Date=Date,R2sqrt=R2sqrt)
>  write.csv(Test,file="Test")
>  #Read in example file
>  filenames="Test"
>  read.zoo(file=filenames, header = TRUE, FUN = as.chron, sep = ",", colClasses = c("NULL", "NULL", "character", "numeric"))
>  lapply(filenames, read.zoo, header = TRUE, FUN = as.chron, sep = ",", colClasses = c("NULL", "NULL", "character", "numeric"))

FUN is an argument of lapply so what is actually running is

   lapply(filenames, FUN = as.chron, ...)

rather than

   lapply(filenames, FUN = read.zoo, ...).

It seems the short form usage of lapply won`t work here.  Try this instead:

   lapply(filenames, function(F) read.zoo(F, header = TRUE, sep = ",",
FUN = as.chron,
     colClasses = c("NULL", "NULL", "character", "numeric")))

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