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Merge and bind homogeneous file arrays

Source: R/bind.R
filearray_bind.Rd

The file arrays to be merged must be homogeneous: same data type, partition size, and partition length

Usage

filearray_bind(
  ...,
  .list = list(),
  filebase = tempfile(),
  symlink = FALSE,
  overwrite = FALSE,
  cache_ok = FALSE
)

Arguments

..., .list

file array instances

filebase

where to create merged array

whether to use file.symlink; if true, then partition files will be symbolic-linked to the original arrays, otherwise the partition files will be copied over. If you want your data to be portable, do not use symbolic-links. The default value is FALSE

overwrite

whether to overwrite when filebase already exists; default is false, which raises errors

cache_ok

see 'Details', only used if overwrite is true.

Value

A bound array in 'FileArray' class.

Details

The input arrays must share the same data type and partition size. The dimension for each partition should also be the same. For example an array x1 has dimension \(100x20x30\) with partition size 1, then each partition dimension is \(100x20x1\), and there are 30 partitions. x1 can bind with another array of the same partition size. This means if x2 has dimension \(100x20x40\) and each partition size is 1, then x1 and x2 can be merged.

If filebase exists and overwrite is FALSE, an error will always raise. If overwrite=TRUE and cache_ok=FALSE, then the existing filebase will be erased and any data stored within will be lost. If both overwrite and cache_ok are TRUE, then , before erasing filebase, the function validates the existing array header and compare the header signatures. If the existing header signature is the same as the array to be created, then the existing array will be returned. This cache_ok could be extremely useful when binding large arrays with symlink=FALSE as the cache might avoid moving files around. However, cache_ok should be enabled with caution. This is because only the header information will be compared, but the partition data will not be compared. If the existing array was generated from an old versions of the source arrays, but the data from the source arrays has been altered, then the cache_ok=TRUE is rarely proper as the cache is outdated.

The symlink option should be used with extra caution. Creating symbolic links is definitely faster than copying partition files. However, since the partition files are simply linked to the original partition files, changing to the input arrays will also affect the merged arrays, and vice versa; see 'Examples'. Also for arrays created from symbolic links, if the original arrays are deleted, while the merged arrays will not be invalidated, the corresponding partitions will no longer be accessible. Attempts to set deleted partitions will likely result in failure. Therefore symlink should be set to true when creating merged arrays are temporary for read-only purpose, and when speed and disk space is in consideration. For extended reading, please check files for details.

Examples

partition_size <- 1
type <- "double"
x1 <- filearray_create(
    tempfile(), c(2,2), type = type,
    partition_size = partition_size)
x1[] <- 1:4
x2 <- filearray_create(
    tempfile(), c(2,1), type = type,
    partition_size = partition_size)
x2[] <- 5:6

y1 <- filearray_bind(x1, x2, symlink = FALSE)
y2 <- filearray_bind(x1, x2)

# y1 copies partition files, and y2 simply creates links 
# if symlink is supported

y1[] - y2[]
#>      [,1] [,2] [,3]
#> [1,]    0    0    0
#> [2,]    0    0    0

# change x1
x1[1,1] <- NA

# y1 is not affected
y1[]
#>      [,1] [,2] [,3]
#> [1,]    1    3    5
#> [2,]    2    4    6

# y2 changes 
y2[]
#>      [,1] [,2] [,3]
#> [1,]    1    3    5
#> [2,]    2    4    6