fwhich {filearray}

A generic function of which that is 'FileArray' compatible

Description

A generic function of which that is 'FileArray' compatible

Usage

fwhich(x, val, arr.ind = FALSE, ret.values = FALSE, ...)

## Default S3 method:
fwhich(x, val, arr.ind = FALSE, ret.values = FALSE, ...)

## S3 method for class 'FileArray'
fwhich(x, val, arr.ind = FALSE, ret.values = FALSE, ...)

Arguments

x

any R vector, matrix, array or file-array

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'

arr.ind

logical; should array indices be returned when x is an array?

ret.values

whether to return the values of corresponding indices as an attributes; default is false

...

passed to val if val is a function

Value

The indices of x elements that are listed in val.

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)
       })