Hello QiangLiu!
If I understand correctly, you would like to just read 5 elements in the 1D
dataset, starting at the 3rd element.
In that case, you would:
- Specify a 1D memory space of 5 elements
- Select (a hyperslab) of 5 elements from the file data space
- Pass in the memory space and file data space to H5Dread. Your read
buffer would be 5 elements in size.
In C, it would look like this:
double rdset_data[5];
...
start [0] = 2;
count [0] = 5;
stride [0] = 1;
block[0] = 1;
status = H5Sselect_hyperslab (dataspace, H5S_SELECT_SET, start, stride,
count, NULL);
dimsm[0] = 5;
memspace = H5Screate_simple (1, dimsm, NULL);
status = H5Dread (dataset_id, H5T_NATIVE_DOUBLE, memspace, dataspace,
H5P_DEFAULT, rdset_data);
See the attached C program for more details.
Let me know if you have more questions!
-Barbara
====================
Barbara Jones
The HDF Helpdesk
The HDF Group
[email protected]
====================
From: Hdf-forum [mailto:[email protected]] On Behalf Of
QiangLiu
Sent: Wednesday, October 16, 2013 8:18 AM
To: Hdf-forum
Subject: [Hdf-forum] Coding with java API to read partial data
Hello:
When I am coding with java API,I meet a question.
If I hava a one-dimensional array(eg:1,2,.....,10),now I want to read
3-7,how can I only use 5 size of space to read data.
My way:
H5.H5Sselect_hyperslab(dataspace_id,
HDF5Constants.H5S_SELECT_SET,start, null, count, null);
H5.H5Dread(dataset_id,
HDF5Constants.H5T_IEEE_F64LE,HDF5Constants.H5S_ALL, filespace_id,
HDF5Constants.H5P_DEFAULT,dset_data);
But dset_data's size hava to be 10,or at least 7.
So how can I use 5 space to read partial data?
Thanks for help
/*
* Writing and reading an existing dataset.
*/
#include <hdf5.h>
#define FILE "dset.h5"
main() {
hid_t dataspace, memspace;
hid_t file_id, dataset_id; /* identifiers */
herr_t status;
hsize_t dims[1], dimsm[1];
int i, j;
double dset_data[10], rdset_data[5];
hsize_t count[1], stride[1], block[1];
hssize_t start[1];
/* Initialize the dataset. */
for (i = 0; i < 10; i++)
dset_data[i] = 10*i;
printf ("\nCreate file, 1D dataset. Write data. Close all.\n");
file_id = H5Fcreate (FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
dims[0] = 10;
dataspace = H5Screate_simple (1, dims, NULL);
dataset_id = H5Dcreate (file_id, "/data1d", H5T_IEEE_F64LE, dataspace,
H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
status = H5Dwrite (dataset_id, H5T_NATIVE_DOUBLE, H5S_ALL, H5S_ALL,
H5P_DEFAULT, dset_data);
status = H5Dclose (dataset_id);
status = H5Sclose (dataspace);
status = H5Fclose (file_id);
printf ("Reopen file and read 5 elements.\n");
file_id = H5Fopen(FILE, H5F_ACC_RDWR, H5P_DEFAULT);
dataset_id = H5Dopen (file_id, "/data1d", H5P_DEFAULT);
dataspace = H5Dget_space (dataset_id);
start [0] = 2;
count [0] = 5;
stride [0] = 1;
block[0] = 1;
status = H5Sselect_hyperslab (dataspace, H5S_SELECT_SET, start, stride,
count, NULL);
dimsm[0] = 5;
memspace = H5Screate_simple (1, dimsm, NULL);
status = H5Dread (dataset_id, H5T_NATIVE_DOUBLE, memspace, dataspace,
H5P_DEFAULT, rdset_data);
for (i=0; i<5; i++)
printf (" %lf", rdset_data[i]);
printf ("\n");
/* Close all. */
status = H5Dclose(dataset_id);
status = H5Sclose (dataspace);
status = H5Sclose (memspace);
status = H5Fclose(file_id);
}
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