h5read#

Purpose#

Reads data from an HDF5 dataset into a GAUSS matrix.

Format#

y = h5read(fname, dname[, dims[, offset]])#
Parameters:

  • fname (string) – a name of the HDF5 file.

  • dname (string) – a name of the dataset in HDF5 file. e.g. "/mydata".

  • dims (Nx1 vector) – where N is the number of dimensions in the dataset, the dimensions of data to read.

  • offset (Nx1 vector) – where N is the number of dimensions in the dataset, the data to skip.

Returns:

y (matrix or array) – the data requested from the file.

Examples#

Basic write then read entire contents of an HDF5 file#

// Define a name of a HDF5 file
fname = "testdata.h5";

// Define a name of a dataset
dname = "/mydata";

// Define a size of 4 rows and 3 columns
r = 3;
c = 2;
dims  = r|c;

// Create a 3x2 fixed dimension dataset in a HDF5 file
call h5create(fname, dname, dims);

// Create a 3x2 matrix
x = { 9 4,
      2 1,
      0 7 };

// Write x to dataset
call h5write(fname, dname, x);

// Read all contents from dataset
y = h5read(fname, dname);

After the code above:

x = 9  4    y = 9  4
    2  1        2  1
    0  7        0  7

Read HDF5 first two rows and first two columns#

// Define a name of a HDF5 file
fname = "testdata.h5";

// Define a name of a dataset
dname = "/mydata";

// Size of data to read
dims = 2|2;

// Read data from file created in Example 1, above
y2 = h5read(fname, dname, dims);

After the code above:

y2 =    9 4
        2 1

Read HDF5 first two rows and first two columns#

// Define a name of a HDF5 file
fname = "testdata.h5";

// Define a name of a dataset
dname = "/mydata";

// Size of data to read
dims = 2|2;

// Dimensions to skip: 1 row and 0 columns
offset = 1|0;

// Read data from file created in Example 1, above
y3 = h5read(fname, dname, dims, offset);

After the code above:

y3 =    2 1
        0 7

Read HDF5 file with offset at more than one dimension#

// Define a name of a HDF5 file
fname = "testdata.h5";

// Define a new dataset name
dname = "/highdimension";

// Create 3 dimensions, with __INFP indicating expandable rows
dims = 3 | __INFP  | 4;

// Define data type
datatype = "double";

// Define chunk size since the second dimension is infinite
chunk_size = 1|128|4;

// Create "highdimension" dataset, inside file created in Example 1 (above)
call h5create(fname, dname, dims, datatype, chunk_size);

// Set seed for repeatable random numbers
rndseed 7672342;

// Create random normal data array, with dimensions 3x10x4
x = areshape(rndn(3 * 10 * 4, 1), 3 | 10 | 4);

// Write it into dataset
call h5write(fname, dname, x);

// Skip first two rows and first column of each
// of the 3 matrices in the 3x10x4 array
offset = 0|2|1;

// Define the read size after removing offset
dims_read = 2|2|2;

// Run h5read function
y4 = h5read(fname, dname, dims_read, offset);

After the code above, we see that y4 is a 2x2x2 (number of dimensions to read dims_read) array, containing the contents of the x, after skipping the dimensions \({ 0, 2, 1 }\) specified in offset:

y4  = Plane [1,.,.]

     -0.61557786      -0.76592868
     -0.30976522       0.11296623

      Plane [2,.,.]

     -0.23144975       -1.1369840
     -0.89682110        1.6684102


x =   Plane [1,.,.]

      -1.2045242       -1.0675179      -0.74403139      -0.72860218
      0.20337032      -0.48451306    -0.0039387096       0.46361645
     -0.57448560      -0.61557786      -0.76592868     -0.032267807
     -0.88033211      -0.30976522       0.11296623        1.2724183
      -1.4409872      -0.90939666       0.22487451      -0.37188053
      -1.5478724      -0.43944280      0.010049938        1.0196427
       1.3352024        1.0734150      -0.98373668      -0.57590137
     -0.32428680       0.53099143      -0.71162764       -2.1188409
     -0.22060808     -0.024172215       0.64942867      -0.51276843
      0.12600180      -0.65155519       -2.2815720        1.4961735

     Plane [2,.,.]

     -0.78337697      -0.52759501       -1.2322159      -0.31936828
     -0.47552440       -1.0708763       0.43111378        1.5146598
      0.54119533      -0.23144975       -1.1369840      -0.11052318
      0.47963176      -0.89682110        1.6684102      -0.43704128
     -0.27511827      -0.65207535      -0.17394561      -0.84737201
     -0.14595989     -0.028056845       0.50018732      -0.76191566
     -0.98846912        1.4389099        1.3716329       -1.3419693
     -0.29630831       -1.2029618       -1.4958204       -2.0829113
     -0.56764971      -0.53397186      -0.95002213      -0.10182348
      -1.6156998       -1.5120152      0.013456774     -0.037790884

     Plane [3,.,.]

      0.42346079      -0.61879151      0.062894922       0.43245351
     0.092322769       0.68876937      -0.61677358        2.8805431
      0.33204968        2.1878476       -1.1113500      -0.38579652
      0.35943828       0.32172778      -0.25074937      -0.34662609
     -0.95053031     0.0010335034      -0.12838005       -1.2333248
      0.59991891       0.73834232      -0.23521782      -0.63566653
      -1.5290045      -0.36202638       0.69077565        1.0898312
      0.71036599      0.086441099      -0.40250335       0.58997554
     -0.55612014      0.084524826       0.60194547       0.26031576
      0.49760949      0.070206385       0.65894867       0.73385573

See also

Functions h5create(), h5write(), open, create, writer(), seekr(), eof()

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