CF data object

This class is a basic ancestor to all classes that contain data from a netCDF resource, specifically data variables and axes. More useful classes use this class as ancestor.

Super class

ncdfCF::CFObject -> CFData

Active bindings

data_type

Set or retrieve the data type of the data in the object. Setting the data type to a wrong value can have unpredictable and mostly catastrophic consequences.

ndims

(read-only) Retrieve the dimensionality of the data in the array.

NC_map

Returns a list with columns "start" and "count" giving the indices for reading the data of this object from a netCDF resource. The list is empty if this object is not backed by a netCDF resource.

Methods

Public methods

• CFData$new()

• CFData$detach()

• CFData$dim()

• CFData$read_data()

• CFData$read_chunk()

Inherited methods

• ncdfCF::CFObject$append_attribute()
• ncdfCF::CFObject$attach_to_group()
• ncdfCF::CFObject$attribute()
• ncdfCF::CFObject$attributes_identical()
• ncdfCF::CFObject$delete_attribute()
• ncdfCF::CFObject$print_attributes()
• ncdfCF::CFObject$set_attribute()
• ncdfCF::CFObject$write_attributes()

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Method new()

Create a new CFData instance. This method is called upon creating CF objects, such as when opening a netCDF resource or creating a new CF object. It is rarely, if ever, useful to call this constructor directly. Instead, use the methods from higher-level classes such as CFVariable.

Usage

CFData$new(
  obj,
  group,
  values,
  start = 1L,
  count = NA,
  attributes = data.frame()
)

Arguments

obj

The NCVariable instance upon which this CF object is based when read from a netCDF resource, or the name for the new CF object to be created.

group

The CFGroup that this instance will live in.

values

Optional. The values of the object in an array. Ignored when argument obj is an NCVariable instance.

start

Optional. Vector of indices where to start reading data along the dimensions of the array on file. The vector must be NA to read all data, otherwise it must have agree with the dimensions of the array on file. Default value is 1, i.e. start from the beginning of the 1-D NC variable. Ignored when argument obj is not an NCVariable instance.

count

Optional. Vector of number of elements to read along each dimension of the array on file. The vector must be NA to read to the end of each dimension, otherwise its value must agree with the corresponding start value and the dimension of the array on file. Default is NA. Ignored when argument obj is not an NCVariable instance.

attributes

Optional. A data.frame with the attributes of the object.

Returns

A CFData instance.

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Method detach()

Detach the current object from its underlying netCDF resource. If necessary, data is read from the resource before detaching.

Usage

CFData$detach()

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Method dim()

Retrieve the dimensions of the data of this object.

Usage

CFData$dim(dimension)

Arguments

dimension

Optional. The index of the dimension to retrieve the length for. If omitted, retrieve the lengths of all dimensions.

Returns

Integer vector with the length of each requested dimension. Read the data of the CF object from the NC file. The data is cached by self so repeated calls do not access the netCDF resource, unless argument refresh is TRUE. This method will not assess how big the data is before reading it so there is a chance that memory will be exhausted. The calling code should check for this possibility and break up the reading of data into chunks.

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Method read_data()

Usage

CFData$read_data(refresh = FALSE)

Arguments

refresh

Should the data be read from file if the object is linked? This will replace current values, if previously loaded. Default FALSE.

Returns

An array of data, invisibly, as prescribed by the start and count values used to create this object. If the object is not backed by a netCDF resource, returns NULL. Read a chunk of raw data of the CF object, as defined by the start and count vectors. Note that these vectors are relative to any subset of the data variable that this CF object refers to. The data read by this method will not be stored in self so the calling code must take a reference to it.

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Method read_chunk()

Usage

CFData$read_chunk(start, count)

Arguments

start

Vector of indices where to start reading data along the dimensions of the array. The vector must be NA to read all data, otherwise it must agree with the dimensions of the array.

count

Vector of number of elements to read along each dimension of the array. The vector must be NA to read to the end of each dimension, otherwise its value must agree with the corresponding start value and the dimension of the array.

Returns

An array of data, as prescribed by the start and count arguments, or NULL if there is no data.