previousblock

Information on previous block in blocked file-set

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Syntax

blkInfo = previousblock(bs)

Description

blkInfo = previousblock(bs) returns the information on the previous block in the BlockedFileSet object bs, then recedes the internal pointer of the blocked file-set to the previous block. Subsequent calls to the previousblock function continue reading from the endpoint of the previous call.

example

Examples

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Open Live Script

Return to a previous block in a blocked file-set to get block information.

Create a blocked file-set bs for a collection of blocks.

folder = {'accidents.mat','airlineResults.mat','census.mat','earth.mat'}
folder = 1×4 cell
    {'accidents.mat'}    {'airlineResults.mat'}    {'census.mat'}    {'earth.mat'}


bs = matlab.io.datastore.BlockedFileSet(folder)
bs = 
  BlockedFileSet with properties:

                   NumBlocks: 4
               NumBlocksRead: 0
                   BlockSize: 'file'
                   BlockInfo: Show BlockInfo for all 4 blocks
    AlternateFileSystemRoots: {}

Get the information for the first block and move the internal pointer forward one block.

blk1 = nextblock(bs)
blk1 = 
  1×1 BlockInfo
                                                        Filename                                                         FileSize    Offset    BlockSize
    _________________________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs2566-0/Bdoc25b.2988451/build/runnable/matlab/toolbox/matlab/demos/accidents.mat"      7343        0         7343

Get information for the second block and move the internal pointer forward one block.

blk2 = nextblock(bs)
blk2 = 
  1×1 BlockInfo
                                       Filename                                        FileSize     Offset    BlockSize 
    ______________________________________________________________________________    __________    ______    __________

    "/tmp/Bdoc25b_2988451_1117187/tpc3b50af4/matlab-ex46270107/airlineResults.mat"    1.5042e+05      0       1.5042e+05

Get information for the second block again and recede the internal pointer to the second block.

prev = previousblock(bs)
prev = 
  1×1 BlockInfo
                                       Filename                                        FileSize     Offset    BlockSize 
    ______________________________________________________________________________    __________    ______    __________

    "/tmp/Bdoc25b_2988451_1117187/tpc3b50af4/matlab-ex46270107/airlineResults.mat"    1.5042e+05      0       1.5042e+05

Input Arguments

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Blocked file-set, specified as a matlab.io.datastore.BlockedFileSet object. To create a BlockedFileSet object, see matlab.io.datastore.BlockedFileSet.

Example: hasPreviousBlock(bs)

Output Arguments

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This property is read-only.

Information about blocks in the BlockedFileSet object, returned as a BlockInfo object with the following properties:

  • Filename — Name of the file in the BlockedFileSet object. The name contains the full path of the file.

  • FileSize — Size of the file in number of bytes.

  • Offset — Starting offset within the file to be read.

  • BlockSize — Size of the block in number of bytes.

Tips

  • The previousblock method returns an error if no blocks have been read from the BlockedFileSet object bs. To avoid this error, you can use previousblock along with hasPreviousBlock and reset. The hasPreviousBlock method checks if blocks still remain that were previously read from the BlockedFileSet object, while the reset method resets the internal pointer to the beginning of the BlockedFileSet object.

Version History

Introduced in R2020a

See Also