Xarray离散散点图：指定图例/颜色顺序

Question

用dataSet dataSet xr.plot.scatter（）在其中产生传奇离散值是任意排序的，对应于每个级别的不可预测的颜色分配。是否可以为给定离散值指定特定的颜色或位置？

一个简单的可重复的示例：

import xarray as xr

# get a predefined dataset
uvz = xr.tutorial.open_dataset("eraint_uvz")

# select a 2-D subset of the data
uvzr = uvz.isel(level=0, month=0, latitude=slice(150, 242),
                longitude=slice(240, 300))

# define a discrete variable based on levels of a continuous variable
uvzr['zone'] = 'A'
uvzr['zone'] = uvzr.zone.where(uvzr.u > 30, other='C')
uvzr['zone'] = uvzr.zone.where(uvzr.u > 10, other='B')

# do the plot
xr.plot.scatter(uvzr, x='longitude', y='latitude', hue='zone')

有没有办法确保从上到下安排传奇条目'a''''，'a'，'b'，'c'，说？还是确保将a分配给蓝色，而b则为橙色？

我知道我可以重置matplotlib颜色循环器的值，但是为此，我首先需要知道将绘制哪个离散值。

我使用xarray v2022 .3.0在Python 3.8.6上。借助Xarray的较早版本（我认为0.16），将级别按字母顺序排列。

Answer 1

我使用xarray.dataset.stack和xr.where（...，drop = true）> xray.dataset.stack

import numpy as np   # for unique, to cycle through values
import matplotlib.pyplot as plt   # to get a legend

# instead of np.unique you could pass an iterable of your choice
# specifying the order
for value in np.unique(uvzr.zone):
    # convert to a 1-D dataframe with a co-ordinate including all
    # unique combinations of latitude-longitude values
    uvzr_stacked = uvzr.stack({'location':('longitude', 'latitude')})

    # now select only those grid points in zone value
    uvzr_stacked = uvzr_stacked.where(uvzr_stacked.zone == value,
                                      drop=True)

    # the plotting function can't see the original dims any more;
    # a new name is required, however
    uvzr_stacked['lat'] = uvzr_stacked.latitude
    uvzr_stacked['lon'] = uvzr_stacked.longitude

    # plot!
    xr.plot.scatter(uvzr_stacked, x='lon', y='lat', hue='zone',
                    add_guide=False)

plt.legend(title='zone')