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h5write

Write data to HDF5 dataset

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Syntax

h5write(filename,ds,data)
h5write(filename,ds,data,start,count)
h5write(filename,ds,data,start,count,stride)

Description

h5write(filename,ds,data) writes data to an entire dataset, ds, in the specified HDF5 file. If the dataset is fixed in size, the amount of data to be written must match the size of the dataset.

example

h5write(filename,ds,data,start,count) writes a subset of data to a dataset, beginning at starting location start, and continuing for count elements. In a multidimensional dataset, count specifies a distance in each direction. h5write extends an extendable dataset along any unlimited dimensions, if necessary.

example

h5write(filename,ds,data,start,count,stride) specifies the spacing between elements, stride, along each dimension of the dataset.

example

Examples

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Open Live Script

Create a 10-by-20 dataset named DS1.

h5create("myfile.h5","/DS1",[10 20])

Write a 10-by-20 array of random numbers to the dataset. Since the dimensions of DS1 are fixed, the amount of data to be written to it must match its size.

mydata = rand(10,20);
h5write("myfile.h5","/DS1",mydata)

Display the contents of the file.

h5disp("myfile.h5")
HDF5 myfile.h5 
Group '/' 
    Dataset 'DS1' 
        Size:  10x20
        MaxSize:  10x20
        Datatype:   H5T_IEEE_F64LE (double)
        ChunkSize:  []
        Filters:  none
        FillValue:  0.000000
Open Live Script

Create a 10-by-20 dataset named DS2.

h5create("myfile.h5","/DS2",[10 20])

Write a 5-by-7 subset of data to the last 5-by-7 block of the dataset. Specify count as [5 7] to match the size of the data you are writing. Specify start as [6 14], because moving count cells from this starting point will end in the last element of the dataset.

mydata = rand(5,7);
h5write("myfile.h5","/DS2",mydata,[6 14],[5 7])
Open Live Script

Write data to a dataset that has an unlimited dimension.

Create a dataset that is unlimited along the second dimension. ChunkSize must be specified to set any dimension of the dataset to Inf.

h5create("myfile.h5","/g2/DS2",[20 Inf],"Chunksize",[5 5]);

Write a 3-by-3 block of data to "/g2/DS2". Begin at the starting point [3 2] and write to the end of the block. You can write data of any size along the second dimension of the dataset, since it is unlimited.

data = rand(3);
start = [3 2];
count = [3 3];
h5write("myfile.h5","/g2/DS2",data,start,count);

Read all of the data from the dataset. 

h5read("myfile.h5","/g2/DS2")
ans = 20×4

         0         0         0         0
         0         0         0         0
         0    0.8147    0.9134    0.2785
         0    0.9058    0.6324    0.5469
         0    0.1270    0.0975    0.9575
         0         0         0         0
         0         0         0         0
         0         0         0         0
         0         0         0         0
         0         0         0         0
      ⋮

Input Arguments

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Filename of an existing HDF5 file, specified as a string scalar or character vector.

Depending on the location of your file, filename can take one of these forms.

Location

Form

Current folder

Specify the name of the file in filename.

Example: "myFile.h5"

Other folders

If the file is not in the current folder or in a folder on the MATLAB® path, then specify the full or relative path in filename.

Example: "C:\myFolder\myFile.h5"

Example: "myFolder\myFile.h5"

Remote location

If the file is stored at a remote location, then filename must contain the full path of the file specified as a uniform resource locator (URL) of the form:

scheme_name://path_to_file/filename

Based on your remote location, scheme_name can be one of the values in this table.

Remote Locationscheme_name
Amazon S3™s3
Windows Azure® Blob Storagewasb, wasbs

For more information, see Work with Remote Data.

Example: "s3://myBucket/myFolder/myFile.h5"

  • If your file consists of several physical files using the Family driver, specify filename using a format specifier. For example, to use the Family driver with the two files family0.h5 and family1.h5, specify filename as "family%d.h5".

  • If your file consists of several physical files using the Multi driver or the Split driver, specify filename as the leading prefix of the names of the physical files. For example, to use the Multi driver with the six files multi-b.h5, multi-g.h5, multi-l.h5, multi-o.h5, multi-r.h5, and multi-s.h5, specify filename as "multi".

Dataset name, specified as a string scalar or character vector containing the name of an existing dataset in the HDF5 file.

Data to be written to the HDF5 file. If a numeric datatype was specified in the corresponding call to h5create, then data is a numeric matrix containing floating-point or integer data. Data must be non sparse, and must be the same size as the HDF5 dataset if you do not specify start or count. If a dimension in the dataset is unlimited, then the data to be written can be any size along that dimension.

If "string" was specified as the datatype in the corresponding call to h5create, data is a MATLAB string array. The string array dimensions must match those specified in the call to h5create.

Starting location, specified as a numeric vector of positive integers. For an n-dimensional dataset, start is a vector of length n containing 1-based indices. The elements of start correspond, in order, to the dataset dimensions. If any dimension of ds is unlimited, you must specify start.

If you do not specify start, then the h5write function starts writing to the dataset from the first index along each dimension.

Number of elements to write, specified as a numeric vector of positive integers. For an n-dimensional dataset, count is a vector of length n, specifying the number of elements to write to the dataset along each dimension. The elements of count correspond, in order, to the dataset dimensions. If any dimension of ds is unlimited, you must specify count.

Spacing between elements along each dimension of the dataset, specified as a numeric vector of integers. For an n-dimensional dataset, stride is a vector of length n. The elements of the stride vector correspond, in order, to the dataset dimensions. A value of 1 writes without skipping elements in the corresponding dimension, a value of 2 writes every other element, and so on.

If you do not specify stride, then the h5write function writes data without skipping along each dimension.

Limitations

  • h5write does not support writing to files stored remotely in HDFS™.

Version History

Introduced in R2011a

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See Also

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