fwhich.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/methods.R
\name{fwhich}
\alias{fwhich}
\alias{fwhich.default}
\alias{fwhich.FileArray}
\title{A generic function of \code{which} that is \code{'FileArray'} compatible}
\usage{
fwhich(x, val, arr.ind = FALSE, ret.values = FALSE, ...)

\method{fwhich}{default}(x, val, arr.ind = FALSE, ret.values = FALSE, ...)

\method{fwhich}{FileArray}(x, val, arr.ind = FALSE, ret.values = FALSE, ...)
}
\arguments{
\item{x}{any R vector, matrix, array or file-array}

\item{val}{values to find, or a function taking one argument (a slice of 
data vector) and returns either logical vector with the same length as the 
slice or index of the slice; see 'Examples'}

\item{arr.ind}{logical; should array indices be 
returned when \code{x} is an array?}

\item{ret.values}{whether to return the values of corresponding indices as 
an attributes; default is false}

\item{...}{passed to \code{val} if \code{val} is a function}
}
\value{
The indices of \code{x} elements that are listed in \code{val}.
}
\description{
A generic function of \code{which} that is \code{'FileArray'} compatible
}
\examples{


# ---- Default case ------------------------------------
x <- array(1:27 + 2, rep(3,3))

# find index of `x` equal to either 4 or 5
fwhich(x, c(4,5))
res <- fwhich(x, c(4,5), ret.values = TRUE)
res
attr(res, "values")

# ---- file-array case --------------------------------
arr <- filearray_create(tempfile(), dim(x))
arr[] <- x
fwhich(arr, c(4,5))
fwhich(arr, c(4,5), arr.ind = TRUE, ret.values = TRUE)

arr[2:3, 1, 1]

# Clean up this example
arr$delete()

# ---- `val` is a function ----------------------------
x <- as_filearray(c(sample(15), 15), dimension = c(4,4))

ret <- fwhich(x, val = which.max, 
              ret.values = TRUE, arr.ind = FALSE)

# ret is the index
ret == which.max(x[])

# attr(ret, "values") is the max value
max(x[]) == attr(ret, "values")

# customize `val`
fwhich(x, ret.values = TRUE, arr.ind = FALSE,
       val = function( slice ) {
           slice > 10 # or which(slice > 10)
       })


}