if y is a pandas series object with 0 and 1, then what does y.values==0,1 or y.values==0,0 means?

Question

y= pd.Series([0,1,0,1,1,0])

In the code below they have used this and i am stuck on this point. what does y.values==0,0 means and how all the other combination are different from one another.

plt.figure(dpi=120)
plt.scatter(pca[y.values==0,0], pca[y.values==0,1], alpha=0.5, label='Edible', s=2)
plt.scatter(pca[y.values==1,0], pca[y.values==1,1], alpha=0.5, label='Poisonous', s=2)
plt.legend()

Answer 1

Suppose the following numpy array pca and Series y:

import pandas as pd
import numpy as np

pca = np.arange(0, 12).reshape(-1, 2)
y = pd.Series([0, 1, 0, 1, 1, 0])

# pca
array([[ 0,  1],
       [ 2,  3],
       [ 4,  5],
       [ 6,  7],
       [ 8,  9],
       [10, 11]])

# y
0    0
1    1
2    0
3    1
4    1
5    0
dtype: int64

To get elements from a 2D array, you have to pass the coordinates of rows and columns you want to get:

# Get rows from pca where y==0 and get the first column (0)
>>> pca[y.values==0, 0]  # or pca[y==0, 0]
array([ 0,  4, 10])

# Get rows from pca where y==0 and get the second column (1)
>>> pca[y.values==0, 1]  # or pca[y==0, 1]
array([ 1,  5, 11])

# This is the same for other scatter line.

Instead of pass selected rows explicitly, here you are using a boolean mask y==0. It means you return another Series with the same length of y with boolean values:

>>> y == 0   # Original
0     True   # 0
1    False   # 1
2     True   # 0
3    False   # 1
4    False   # 1
5     True   # 0
dtype: bool