GetItem

class baseband_tasks.shaping.GetItem(ih, item)

Bases: ChangeSampleShapeBase

Index or slice the samples of a stream.

Useful to select, e.g., a specific frequency band or polariazation.

Parameters:

ihtask or baseband stream reader

Input data stream.

itemint, slice, list of int, or array of int

Anything that can slice a numpy array. Should only attempt to slice the samples, not the time axis.

See also

GetSlice

slice the time axis and index or slice the samples

Reshape

to reshape the samples

Transpose

to transpose sample axes

ReshapeAndTranspose

to reshape the samples and transpose the axes

ChangeSampleShape

to change the samples with a user-supplied function.

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 with just the first three channels kept, one could do:

>>> import numpy as np, astropy.units as u, baseband
>>> from baseband_tasks.shaping import GetItem
>>> 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)
>>> gih = GetItem(fh, slice(0, 6))
>>> gih.read(2).shape
(2, 6)
>>> gih.polarization
array(['L', 'R', 'L', 'R', 'L', 'R'], dtype='<U1')
>>> gih.frequency
<Quantity [311.25, 311.25, 327.25, 327.25, 343.25, 343.25] MHz>
>>> gih.sideband
array(1, dtype=int8)
>>> fh.close()

Methods Summary

task(data)

Get the preset item from the data.

Methods Documentation

task(data)

Get the preset item from the data.