Re: array with NA values

[Eric yang <yang_eric9@yahoo.com>]

Thanks for the email Tim.

I forgot to mention that at the end of performing the calculations on the non-missing elements, I need to construct the original array which will be populated with the new numbers and all missing values remain the same.

Any help is appreciated.


Tim Hesterberg <timh@insightful.com> wrote:
>  My apologies; I used my own function "omit.na" in the example below.
> Thanks to Chris Barker for noticing this.
>
> omit.na <- function(x) x[!is.na(x)]
>
> Tim Hesterberg
>
>
> >If you are doing many operations with the same data, you might
> >want to convert your data into a list with missing values omitted.
> >Each element of the list would be a vector containing non-missing values.
> >Optionally, you can give the list dimensions.
> >
> >x <- array(1:1000,
>  c(10,10,10))
> >set.seed(0)
> >x[runif(1000) > .4] <- NA
> >
> >temp <- x
> >dim(temp) <-  c(10, prod(dim(x)[2:3]))
> >x2 <- lapply(1:ncol(temp), function(j, x) omit.na(x[,j]), x = temp)
> >x2  # list of length 100, containing non-missing values for each
> >
> ># Now can turn x2 into a matrix/list hybrid if you like,
> ># to let you use apply on rows or columns
> >dim(x2) <- dim(x)[2:3]
> >
> ># example using apply:
> >apply(x2, 2, function(x) length(unlist(x)))
> >
> >Tim Hesterberg
> >
> >>Dear all,
> >>
> >>I have numerous 3-dimenional arrays and each array contains no entire row or column with NA values. However, 50-60% of the values in the array are NA values. I perform various operations on the array using the apply statement. However, because the arrays are quite large the calculations take a while to finish. Within the apply statement I reduce the number of
>  calculations on the vector by using the !is.na() statement. Is there a faster way to run the apply command without the need to read in an enitire vector from the array which contains a large amount of NA values, i.e. should I store the data in another format to avoid having an array with a large amount of NA values.
> >>
> >>For example, if I have a 3-dimensional 1000x1000x1000 and use the apply statement on dimensions 2 and 3, I'm reading in vectors of length 1000 in the apply statement and most of the 1000 values might be NAs. Can this be avoided?
> >>
> >>I would greatly appreciate any help on this.
> >>Dave
> >
>
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