Set initial slider position in Hyperslicer

[EvdWee]

Hello,

I am using hyperslicer to visualize an image stack (3D array) and navigate through the stack. This works nicely, but I would like to set the initial position of the slider to a specific value, not just the first image in the stack.

How to do this with the hyperslicer() function? My code looks something like this:

fig = plt.figure(figsize=(9,9))

control1 = hyperslicer(array,vmin=np.min(array), vmax=np.max(array))

plt.show()

[EvdWee]

I have found the dictionary with the slider position, and can modify it, but it does not update the slider position:

[ianhi]

Hi @EvdWee I'm glad youre finding it useful!

Unfortunately the inability to set initial positions is one of the longstanding issues with this library that turns out to be surprisingly complicated to fix. See more details here: #183

That said you can hopefully use the below set_param_indices function to accomplish what you want:

%matplotlib ipympl

import matplotlib.pyplot as plt
import numpy as np

from mpl_interactions import hyperslicer


def set_param_indices(controls, setters: dict[str, int] = None, **kwargs):
    """
    Set initial values of sliders assuming that you
    are creating ipywidgets sliders, not Matpotlib sliders.

    Parameters
    ----------
    controls : controls object
    setters : dict
        A dictionary of names mapping to indices. Necessary in case one of the slider
        names is invalid as a kwarg to function (e.g. if it has a space in it).
    ** kwargs:
        pairs of param names and index to set the slider to.
        NOTE: the values must be integer indices, not necessarily the
        value that you expect the slider to display.
    """

    if setters is not None:
        kwargs.update(setters)
    for name, idx in kwargs.items():
        controls.controls[name].children[0].value = idx


fig = plt.figure()

array = np.random.rand(5, 2, 512, 512)
control1 = hyperslicer(
    array, vmin=np.min(array), vmax=np.max(array), names=("Z Position", "channel")
)

# can set either using setters or kwargs
set_param_indices(control1, setters={"Z Position": 3}, channel=1)
plt.show()

note: This is setting the index, not the value. So in the case in hyperslicer yo uhave where the z indices map to values you need to set the index that would correspond to 0.9 rather than setting 0.9.

I'm sorry this is confusing, it's all a consequence of design choices I made several years ago that made sense at the time but have made things difficult now :(

[EvdWee]

Thanks for the quick response. This function seems to be a bit more trustworthy than my fix I just found:
control1.vbox.children[0].children[0].value=3