我一直在完成微软的DAT210X-使用Python进行数据科学编程课程。
在创建用于机器学习的SVC模型时,我们被鼓励将数据集X拆分为测试和训练集,并在执行预处理(例如缩放)和降维(例如PCA / Isomap)之前使用sci-kit learn中的train_test_split。下面是我写的解决方案的部分代码示例。
然而,似乎在将X拆分为测试和训练集之前对X进行预处理和PCA / IsoMap更快,并且得分更高。
我的问题是:
1)为什么我们不能切出标签(y),并在将X拆分为测试和训练集之前对所有X进行预处理和降维?
2)对于所有X(减去y),预处理和降维得分比拆分X然后进行预处理和降维要高。这可能是为什么?
X_train, X_test, y_train, y_test = train_test_split(X, y,test_size=0.30, random_state=7)
step_c = .05
endpt_c = 2 + step_c
startpt_c = .05
step_g = .001
endpt_g = .1 + step_g
startpt_g = .001
bestscore = 0.0
best_i = 0.0
best_j = 0.0
pre_proc = [
preprocessing.Normalizer(),
preprocessing.MaxAbsScaler(),
preprocessing.MinMaxScaler(),
preprocessing.KernelCenterer(),
preprocessing.StandardScaler()
]
best_proc = ''
best_score = 0
print('running......')
# pre-processing (scaling etc)
for T in pre_proc:
X_train_T = T.fit_transform(X_train)
X_test_T = T.transform(X_test) # only apply transform to X_test!
# dimensionality reduction
for k in range(2, 6):
for l in range(4, 7):
iso = Isomap(n_neighbors = k, n_components = l)
X_train_iso = iso.fit_transform(X_train_T)
X_test_iso = iso.transform(X_test_T)
# SVC parameter sweeping
for i in np.arange(startpt_c,endpt_c, step_c):
# print(i)
for j in np.arange(startpt_g,endpt_g, step_g):
clf = SVC(C=i, gamma=j , kernel='rbf'
# max_iter=-1, probability=False, random_state=None, shrinking=True, tol=0.001, verbose=False)
)
clf.fit(X_train_iso, y_train)
score = clf.score(X_test_iso, y_test)
if bestscore < score:
bestscore = score
best_c = i
best_g = j
best_proc = T
best_n_neighbors = k
best_n_components = l
# Print final variables that gave best score:
print('proc: ' + str(T), 'score:' + str(bestscore), 'C: ' + str(i), 'g: ' + str(j), 'n_neigh: ' + str(k), 'n_comp: ' + str(l))enter code here