Datasets are objects that a composed of a homogenous collection of data elements. Each dataset has a type that specifies the structure of the individual elements (float, string, compound, etc.), and a shape that specifies the layout of the data elements (scalar, one-dimensional, multi-dimensional). In addition meta-data can be attached to a dataset in the form of attributes. See: Attributes.
Use the POST Dataset operation to create new datasets. As part of the POST request, JSON descriptions for the type and shape of the dataset are included with the request. Optionally, creation properties can be used to specify the chunk layout (how the data elements are stored in the server) and compression filter (e.g. GZIP, LZF, SZIP).
Getting information about a dataset¶
Use the GET Dataset operation to retrieve information about a datasets type, shape, creation properties, and number of attributes. To list all the datasets within a domain use GET Datasets. To list the datasets linked to a particular group use GET Links and look at links with a “collection” key of “datsets”.
Writing data to a dataset¶
To write data into the dataset, use the PUT Value operation. The request can either provide values for the entire dataset, or values for a hyperslab (rectangular sub-region) selection. In addition, if it desired to update a specific list of data elements, a point selection (series of element coordinates) can be passed to the PUT Value operation.
Reading data from a dataset¶
To read either the entire dataset, or a specified selection, use the GET Value operation. Without any request parameters, the GET operation retuns all data values. To read a specific hyperslab, use the select parameter to start and end indexes of the hyperslab (the selection can also include a step value to include a regular subset of the hyperslab). Finally, for one-dimensional datasets with compound types, a where parameter can be used to select elements meeting a specified condition.
To read a specific list of elements (by index values), use the POST Value operation (POST is used in this case rather than GET since the point selection values may be to large to include in the URI.)
If one or more of the dimensions of a dataset may need to be extended after creation, provide a maxdims key to the shape during creation (see POST_dataset). If the value of the maxdims dimension is 0, that dimension is unlimited and may be extended as much as desired. If an upper limit is known, use that value in maxdims which will allow that dimension to be extended up to the given value. To resize the dataset, use PUT_DataShape.rst operation with the desired shape value(s) for the new dimensions.
Note: dimensions can only be increased, not decreased.
The DELETE Dataset operation will remove the dataset, its attributes, and any links to the object.