Map Feature

mapfeature.py

def map_feature(x1, x2):
    '''
    Maps the two input features to quadratic features.

    Returns a new feature array with more features, comprising of
    X1, X2, X1 ** 2, X2 ** 2, X1*X2, X1*X2 ** 2, etc...

    Inputs X1, X2 must be the same size
    '''
    x1.shape = (x1.size, 1)
    x2.shape = (x2.size, 1)
    degree = 6
    out = ones(shape=(x1[:, 0].size, 1))

    m, n = out.shape

    for i in range(1, degree + 1):
        for j in range(i + 1):
            r = (x1 ** (i - j)) * (x2 ** j)
            out = append(out, r, axis=1)

    return out

#load the dataset
data = loadtxt('ex2data2.txt', delimiter=',')

X = data[:, 0:2]
y = data[:, 2]

pos = where(y == 1)
neg = where(y == 0)
scatter(X[pos, 0], X[pos, 1], marker='o', c='b')
scatter(X[neg, 0], X[neg, 1], marker='x', c='r')
xlabel('Microchip Test 1')
ylabel('Microchip Test 2')
legend(['y = 1', 'y = 0'])
#show()

m, n = X.shape

y.shape = (m, 1)

it = map_feature(X[:, 0], X[:, 1])