如何在同一图表上使用 matplotlib 到 plot 2 组 (x,y) 值作为散点 plot（由线连接）？

Question

I have two numpy arrays s1 & s2 each containing a set of (x,y) values.

For example

 ------s1-----
 [[ 0.5         0.        ]
 [ 0.5         0.28284271]
 [ 0.48        0.56568542]
 [ 0.44        0.83721443]
 [ 0.3808      1.08611602]
 [ 0.304       1.30152903]
 [ 0.211968    1.47349739]
 [ 0.107776    1.5934046 ]
 [-0.00489472  1.65437192]
 [-0.12187648  1.65160304]
 [-0.23866245  1.5826593 ]
 [-0.35057336  1.44765143]
 [-0.45293778  1.24933718]
 [-0.54127926  0.99311688]
 [-0.61150322  0.6869231 ]
 [-0.66007602  0.34100464]
 [-0.68418869 -0.03239075]
 [-0.68189832 -0.41942632]
 [-0.6522404  -0.80516626]
 [-0.59530655 -1.17412915]
 [-0.51228308 -1.51088539]]

-----s2----
[[-0.5         0.        ]
 [-0.5         0.28284271]
 [-0.52        0.56568542]
 [-0.56        0.83721443]
 [-0.6192      1.08611602]
 [-0.696       1.30152903]
 [-0.788032    1.47349739]
 [-0.892224    1.5934046 ]
 [-1.00489472  1.65437192]
 [-1.12187648  1.65160304]
 [-1.23866245  1.5826593 ]
 [-1.35057336  1.44765143]
 [-1.45293778  1.24933718]
 [-1.54127926  0.99311688]
 [-1.61150322  0.6869231 ]
 [-1.66007602  0.34100464]
 [-1.68418869 -0.03239075]
 [-1.68189832 -0.41942632]
 [-1.6522404  -0.80516626]
 [-1.59530655 -1.17412915]
 [-1.51228308 -1.51088539]]

I want to plot the x and y values of these arrays such that I get something like this:

With s1 in Blue and s2 in Red.

The code snippet I implemented looked something like this

import matplotlib.pyplot as plt

.
.
.
.

plt.scatter(s1[:][0],s1[:][1],'-o',color='b')
plt.scatter(s2[:][0],s2[:][1],'-x',color='r')
plt.grid(True)
plt.xlabel("x") 
plt.ylabel("y")
plt.show()

I get an error saying:

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\pyplot.py", line 2890, in scatter
    __ret = gca().scatter(

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\__init__.py", line 1438, in inner
    return func(ax, *map(sanitize_sequence, args), **kwargs)

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\cbook\deprecation.py", line 411, in wrapper
    return func(*inner_args, **inner_kwargs)

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\axes\_axes.py", line 4488, in scatter
    collection = mcoll.PathCollection(

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\collections.py", line 955, in __init__
    self.set_sizes(sizes)

  File "C:\Users\Acer\anaconda3\lib\site-packages\matplotlib\collections.py", line 922, in set_sizes
    scale = np.sqrt(self._sizes) * dpi / 72.0 * self._factor

TypeError: ufunc 'sqrt' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

I don't get what went wrong since there is no sqrt in the scatter values and s1 and s2 are float arrays anyway.

Answer 1

You have 2 problems here:

1: You're using the syntax for plt.plot rather than plt.scatter so the third argument is being interpreted as a number for the marker size . If you want to connect the points you should use plt.plot .

2a: Assuming s1 and s2 are numpy.ndarray objects you include all indices in the square brackets and seperatre them with commas.

#import numpy as np
#import matplotlib.pyplot as plt
s1 = np.array(s1)
s2 = np.array(s2)

plt.plot(s1[:,0],s1[:,1],'-o',color='b')
plt.plot(s2[:,0],s2[:,1],'-x',color='r')
plt.grid(True)
plt.xlabel("x") 
plt.ylabel("y")
plt.show()

2b: If however, they are lists of lists , you need to construct lists from the first/second element of each member list. s1[:] with return the whole list, so s1[:][0] will return the first element of the whole list, equal to [0.5, 0] .

One way this can be done with list comprehensions is:

#import matplotlib.pyplot as plt


plt.plot(s1[:,0],s1[:,1],'-o',color='b')
plt.plot(s2[:,0],s2[:,1],'-x',color='r')
plt.grid(True)
plt.xlabel("x") 
plt.ylabel("y")
plt.show()

Both generate the following graph: