import numpy as np
import holoviews as hv
hv.extension('bokeh')
An NdOverlay
is a multi-dimensional dictionary of HoloViews elements presented overlayed in the same space. An NdOverlay
can be considered as a special-case of HoloMap
that can only hold a single type of element at a time. Unlike a regular Overlay
that can be built with the *
operator, the items in an NdOverlay
container have corresponding keys and must all have the same type. See the Building Composite Objects user guide for details on how to compose containers.
NdOverlay
holds dictionaries¶Using the sine_curve
function below, we can declare a dictionary of Curve
elements, where the keys correspond to the frequency values:
frequencies = [0.5, 0.75, 1.0, 1.25]
def sine_curve(phase, freq):
xvals = [0.1* i for i in range(100)]
return hv.Curve((xvals, [np.sin(phase+freq*x) for x in xvals]))
curve_dict = {f:sine_curve(0,f) for f in frequencies}
We now have a dictionary where the frequency is the key and the corresponding curve element is the value. We can now turn this dictionary into an NdOverlay
by declaring the keys as corresponding to the frequency key dimension:
ndoverlay = hv.NdOverlay(curve_dict, kdims='frequency')
ndoverlay
Note that the NdOverlay
is displayed with a legend using colors defined by the Curve
color cycle. For more information on using Cycle
to define color cycling, see the User Guide.
NdOverlay
is multi-dimensional¶By using tuple keys and making sure each position in the tuple is assigned a corresponding kdim
, NdOverlays
allow visualization of a multi-dimensional space:
curve_dict_2D = {(p,f):sine_curve(p,f) for p in [0, np.pi/2] for f in [0.5, 0.75]}
ndoverlay = hv.NdOverlay(curve_dict_2D, kdims=['phase', 'frequency'])
ndoverlay
NdOverlay
is similar to HoloMap
¶Other than the difference in the visual semantics, whereby NdOverlay
displays its contents overlaid, NdOverlay
are very similar to HoloMap
(see the HoloMap
notebook for more information).
One way to demonstrate the similarity of these two containers is to cast our ndoverlay
object to HoloMap
and back to an NdOverlay
:
hmap = hv.HoloMap(ndoverlay)
hmap + hv.NdOverlay(hmap)