python-numpy-方差、相关系数

# Array of differences to mean: differences
differences=versicolor_petal_length-np.mean(versicolor_petal_length)

# Square the differences: diff_sq
diff_sq=np.square(differences)

# Compute the mean square difference: variance_explicit
variance_explicit=np.mean(diff_sq)

# Compute the variance using NumPy: variance_np
variance_np=np.var(versicolor_petal_length)

# Print the results
print(variance_explicit,variance_np)

def pearson_r(x, y):
"""Compute Pearson correlation coefficient between two arrays."""
# Compute correlation matrix: corr_mat
corr_mat=np.corrcoef(x,y)

# Return entry [0,1]
return corr_mat[0,1]

# Compute Pearson correlation coefficient for I. versicolor: r
r=pearson_r(versicolor_petal_length, versicolor_petal_width)

# Print the result
print(r)