HoloViews/Panel - 类型错误：* 不支持的操作数类型：“函数”和“点”

Question

我正在尝试在holoviews.operation.datashader.spread操作上创建参数px ，该参数可以交互更改，并带有一个额外的覆盖层。

pn.bind(get_spreaded, px=px_slider) is working as expected when executing with 。

但是有一个额外的覆盖，行pn.Column(px_slider, interactive * other)报告TypeError: unsupported operand type(s) for *: 'function' and 'Points' 。

如何将*运算符与从pn.bind(...)返回的 function 一起使用？

或者这是错误的方法吗？ 有更好更简单的解决方案吗？

我在 jupyter 实验室中运行了以下代码：

import holoviews as hv
import panel as pn
import numpy as np
from holoviews.operation.datashader import rasterize, spread
import colorcet
import pandas as pd

hv.extension('bokeh')
pn.extension()

hv.opts.defaults(
    hv.opts.Path(width=800, height=400),
    hv.opts.Image(width=800, height=400)
)

def random_walk(n, f=200):
    """Random walk in a 2D space, smoothed with a filter of length f"""
    xs = np.convolve(np.random.normal(0, 0.1, size=n), np.ones(f)/f).cumsum()
    ys = np.convolve(np.random.normal(0, 0.1, size=n), np.ones(f)/f).cumsum()
    xs += 0.1*np.sin(0.1*np.array(range(n-1+f))) # add wobble on x axis
    xs += np.random.normal(0, 0.005, size=n-1+f) # add measurement noise
    ys += np.random.normal(0, 0.005, size=n-1+f)
    return np.column_stack([xs, ys])

# create a path and plot it
path = hv.Path([random_walk(10000, 30)])
path

# rasterize and show the plot
rasterized = rasterize(path).opts(colorbar=True, cmap=colorcet.fire, cnorm='log')
rasterized

# the callback for getting the spreaded plot
def get_spreaded(px=3, shape='circle'):
    return spread(rasterized, px=px, shape=shape)

# show the plot returned from the callback
get_spreaded()

# create the slider for interactively changing the px value
px_slider = pn.widgets.IntSlider(name='Number of pixels to spread on all sides', start=0, end=10, value=3, step=1)

# bind the slider to the callback method
interactive = pn.bind(get_spreaded, px=px_slider)

# show only one plot without any overlay
pn.Column(px_slider, interactive)

# create data for an overlay
df = pd.DataFrame(data={'c1': [1, 2, 3, 4, 5], 'c2': [3, 4, 5, 6, 7]})
other = hv.Points(data=df)
other

# show both plots
pn.Column(px_slider, interactive * other)

最后一行导致以下错误消息：

# 

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[159], line 1
----> 1 pn.Column(px_slider, interactive * other)

TypeError: unsupported operand type(s) for *: 'function' and 'Points'

我希望有某种方法可以包装 function 并可以使用*运算符。 但我还没有找到办法。

Answer 1

虽然在这种特殊情况下，function 的返回值是 HoloViews 可以（原则上）与其他 plot 重叠的东西，但 HoloViews 不知道； HoloViews *运算符只知道如何处理 HoloViews 对象（Elements、HoloMaps、Layouts 和 DynamicMaps），而不是绑定的 Panel 函数。

您可以像使用pn.bind一样使用 DynamicMap，但此处 HoloViews 操作已经了解如何处理 Panel 小部件，因此您可以简单地将小部件提供给spread操作（或任何其他操作的参数）：

import panel as pn, numpy as np, holoviews as hv, colorcet, pandas as pd
from holoviews.operation.datashader import rasterize, spread

hv.extension('bokeh')
pn.extension()

hv.opts.defaults(
    hv.opts.Path(width=800, height=400),
    hv.opts.Image(width=800, height=400)
)

def random_walk(n, f=200):
    """Random walk in a 2D space, smoothed with a filter of length f"""
    xs = np.convolve(np.random.normal(0, 0.1, size=n), np.ones(f)/f).cumsum()
    ys = np.convolve(np.random.normal(0, 0.1, size=n), np.ones(f)/f).cumsum()
    xs += 0.1*np.sin(0.1*np.array(range(n-1+f))) # add wobble on x axis
    xs += np.random.normal(0, 0.005, size=n-1+f) # add measurement noise
    ys += np.random.normal(0, 0.005, size=n-1+f)
    return np.column_stack([xs, ys])

# create plot with interactively controlled spreading
px_slider = pn.widgets.IntSlider(name='Number of pixels to spread on all sides', 
                                 start=0, end=10, value=3, step=1)

path = hv.Path([random_walk(10000, 30)])
rasterized = rasterize(path).opts(colorbar=True, cmap=colorcet.fire, cnorm='log')
spreaded= spread(rasterized, px=px_slider, shape='circle')

# create data for an overlay
df = pd.DataFrame(data={'c1': [1, 2, 3, 4, 5], 'c2': [3, 4, 5, 6, 7]})
other = hv.Points(data=df)

# show both plots
pn.Column(px_slider, spreaded * other)