ChangeSampleShape

class baseband.tasks.ChangeSampleShape(ih, task, method=None, **kwargs)

Bases: Task, ChangeSampleShapeBase

Change sample shape using a callable.

Parameters:

ihtask or baseband stream reader

Input data stream.

taskcallable

The function or method-like callable. The task must work with any number of data samples and change the sample shape only. It will also be applied to the frequency, sideband, and polarization attributes of the underlying stream (if present).

methodbool, optional

Whether task is a method (two arguments) or a function (one argument). Default: inferred by inspection.

See also

Reshape

to reshape the samples

Transpose

to transpose sample axes

ReshapeAndTranspose

to reshape the samples and transpose the axes

GetItem

index or slice the samples

GetSlice

slice the time axis and index or slice the samples

Examples

The VDIF example file from Baseband has 8 threads which contain 4 channels and 2 polarizations, with very little data in the last channel. To produce a stream in which the sample axes are frequency and polarization and only the first three channels are kept, one could do:

>>> import numpy as np, astropy.units as u, baseband
>>> from baseband_tasks.shaping import ChangeSampleShape
>>> fh = baseband.open(baseband.data.SAMPLE_VDIF)
>>> fh.frequency = 311.25 * u.MHz + (np.arange(8.) // 2) * 16. * u.MHz
>>> fh.sideband = 1
>>> fh.polarization = np.tile(['L', 'R'], 4)
>>> sh = ChangeSampleShape(
...    fh, lambda data: data.reshape(-1, 4, 2)[:, :3])
>>> sh.read(2).shape
(2, 3, 2)
>>> sh.polarization
array(['L', 'R'], dtype='<U1')
>>> sh.frequency  
<Quantity [[311.25],
           [327.25],
           [343.25]] MHz>
>>> sh.sideband
array(1, dtype=int8)
>>> fh.close()

Attributes Summary

closed
complex_data
dtype	Data type of the output.
meta
ndim	Number of dimensions of the output.
offset
sample_rate	Number of complete samples per second.
sample_shape	Shape of a complete sample.
samples_per_frame	Number of samples per frame of data.
shape	Shape of the output.
size	Number of component samples in the output.
start_time	Start time of the output.
stop_time	Time at the end of the output, just after the last sample.
time	Time of the sample pointer's current offset in the output.

Methods Summary

close()	Close task.
read([count, out])	Read a number of complete samples.
seek(offset[, whence])	Change the sample pointer position.
tell([unit])	Current offset in the file.

Attributes Documentation

closed = False

complex_data

dtype

Data type of the output.

meta

ndim

Number of dimensions of the output.

offset = 0

sample_rate

Number of complete samples per second.

sample_shape

Shape of a complete sample.

samples_per_frame

Number of samples per frame of data.

For compatibility with file readers, to help indicate what a nominal chunk of data is.

shape

Shape of the output.

size

Number of component samples in the output.

start_time

Start time of the output.

See also time and stop_time.

stop_time

Time at the end of the output, just after the last sample.

See also start_time and time.

time

Time of the sample pointer’s current offset in the output.

See also start_time and stop_time.

Methods Documentation

close()

Close task.

Note that this does not explicitly close the underlying source; instead, it just deletes the reference to it.

read(count=None, out=None)

Read a number of complete samples.

Parameters:

countint or None, optional

Number of complete samples to read. If None (default) or negative, the number of samples left. Ignored if out is given.

outNone or array, optional

Array to store the samples in. If given, count will be inferred from the first dimension; the remaining dimensions should equal sample_shape.

Returns:

outndarray of float or complex

The first dimension is sample-time, and the remaining ones are as given by sample_shape.

seek(offset, whence=0)

Change the sample pointer position.

This works like a normal filehandle seek, but the offset is in samples (or a relative or absolute time).

Parameters:

offsetint, Quantity, or Time

Offset to move to. Can be an (integer) number of samples, an offset in time units, or an absolute time. For the latter two, the pointer will be moved to the nearest integer sample.

whence{0, 1, 2, ‘start’, ‘current’, or ‘end’}, optional

Like regular seek, the offset is taken to be from the start if whence=0 (default), from the current position if 1, and from the end if 2. One can alternativey use ‘start’, ‘current’, or ‘end’ for 0, 1, or 2, respectively. Ignored if offset is a time.

tell(unit=None)

Current offset in the file.

Parameters:

unitUnit or str, optional

Time unit the offset should be returned in. By default, no unit is used, i.e., an integer enumerating samples is returned. For the special string ‘time’, the absolute time is calculated.

Returns:

offsetint, Quantity, or Time

Offset in current file (or time at current position).