I want to plot multiple subplots of scatter plots inside a function, after calling the *args parameter to unpack (x,y) input values. However, I keep getting a simple error:

ValueError: s must be a scalar, or float array-like with the same size as x and y

I cannot seem to solve it even after changing the function into alternative orders of args. Here is my sample code:

import pandas as pd
import numpy as np
from matplotlib.pyplot import plt

x = np.array([[1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4], 
              [0.3, 0.5, 0.6, 0.2, 0.4, 0.5, 0.6, 0.5, 0.8, 0.9, 0.9, 0.8, 0.2, 0.1, 0.5, 0.6],
              ['r', 'r', 'r', 'r', 'r', 'r', 'r', 'r', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b']])


values = pd.DataFrame(x.T, columns=['a', 'b', 'c'])

X = values[values['c'] == 'r'].iloc[ : , 0:2 ].values
Y = values[values['c'] == 'b'].iloc[ : , 0:2 ].values

def test(*args):
    figs, axs = plt.subplots( 1 , 2 , figsize = ( 8 , 8 ) )
    for xy , ax in zip( args , axs.flat ) :
        print(xy)
        ax.scatter(*xy)

test(X, Y)

plt.show()

CodePudding user response：

I have achieved it with the follow, so perhaps there is a cleaner alternative?

def test(*args):
    figs, axs = plt.subplots( 1 , 2 , figsize = ( 8 , 8 ) )
    xy = np.array(args)
    for x_y , ax in zip( xy , axs.flat ) :
        (x, y) = np.hsplit(np.ndarray.flatten(x_y), 2)
        ax.scatter(x, y)

test(X, Y)

plt.show()

CodePudding user response：

okay ... this is the solution to your problem ... this is probably as incomprehensible as your code.

def t(*args):
    figs, axs = plt.subplots( 1 , 2 , figsize = ( 8 , 8 ) )
    for xy , ax in zip( zip(*args) , axs.flat ) :
        print(xy)
        ax.scatter(*xy)

t(X.transpose(), Y.transpose())

now let's convert this to python code... you should know everything about the function just by looking at the function, so *args is useful for something "extra" than the intended behavior of the function.

1. separate X and Y from args, because they are used inside the function explicitly.
2. avoid zip unless the arguments are simple, while nesting generators is performant it's bad for code quality, in your case i'd go for enumerate instead since i am indexing into an array, which needs to be as descriptive as possible.
3. make your calls descriptive, *xy is not descriptive, what is this variable ? is it a tuple ? an ndarray ? what will unpacking it result in ? if you are passing X and Y in it then pass X and Y directly.

def t(*args):
    X,Y = args
    figs, axs = plt.subplots(1, 2, figsize=(8, 8))
    for i, ax in enumerate(axs):
        print(X[:, i], Y[:, i])
        ax.scatter(X[:, i], Y[:, i])

t(X, Y)