matplotlib：在 3D 轴上绘制路径

Question

I would like to plot the path based on xyz location data. Below is a reproducible example, all the lines keep starting from 0 instead of following one after each other.

import seaborn as sns
# loading sample data and replicating my scenario 
data = sns.load_dataset("iris")
# giving it a numeric value to replicate my scenario 
cat_lbl = {'setosa': 1, 'versicolor': 2,'virginica' : 3}
data['cat_lbl'] = data['species'].map(cat_lbl)


#plot headings
species = ['setosa', 'versicolor', 'virginica']


import matplotlib as mpl
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt

sepal_length = data.loc[:,['sepal_length','cat_lbl']]
sepal_width = data.loc[:,['sepal_width','cat_lbl']]
petal_length = data.loc[:,['petal_length','cat_lbl']]

fig = plt.figure(figsize=([20,15]))
for lbl in range(3):
    lbl=lbl+1
    x=sepal_length[(sepal_length.cat_lbl == lbl)].values
    y=sepal_width[(sepal_width.cat_lbl == lbl)].values
    z=petal_length[(petal_length.cat_lbl == lbl)].values


    ax=fig.add_subplot(3,3,lbl, projection='3d')
    ax.plot(x.flatten(),y.flatten(),z.flatten())
    ax.set_title(species[lbl-1])
plt.show()

Answer 1

Your problem is that

x=sepal_length[(sepal_length.cat_lbl == lbl)].values
y=sepal_width[(sepal_width.cat_lbl == lbl)].values
z=petal_length[(petal_length.cat_lbl == lbl)].values

are actually 2D arrays that contain the category index (1,2,3). So when you flatten x.flatten() , you alternate between the coordinate and the category index (you can see that the lines actually loop back to (1,1) on the first graph, (2,2) on the second and (3,3) on the third)

Here is how I would write your code:

import seaborn as sns
import matplotlib as mpl
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt

data = sns.load_dataset("iris")
species = ['setosa', 'versicolor', 'virginica']

fig,axs = plt.subplots(1,3,subplot_kw=dict(projection='3d'),figsize=(9,3))
for sp,ax in zip(species, axs.flat):
    temp = data.loc[data['species']==sp]
    x=temp['sepal_length'].values
    y=temp['sepal_width'].values
    z=temp['petal_length'].values

    ax.plot(x,y,z)
    ax.set_title(sp)
plt.show()

Answer 2

Try ax.plot3D(...) instead of ax.plot(...) as indicated in this tutorial for 3D plotting:

ax = plt.axes(projection='3d')

# Data for a three-dimensional line
zline = np.linspace(0, 15, 1000)
xline = np.sin(zline)
yline = np.cos(zline)
ax.plot3D(xline, yline, zline, 'gray')

# Data for three-dimensional scattered points
zdata = 15 * np.random.random(100)
xdata = np.sin(zdata) + 0.1 * np.random.randn(100)
ydata = np.cos(zdata) + 0.1 * np.random.randn(100)
ax.scatter3D(xdata, ydata, zdata, c=zdata, cmap='Greens');