Keras: Prediction

Sumber: https://machinelearningmastery.com/how-to-make-classification-and-regression-predictions-for-deep-learning-models-in-keras/

Setelah kita memilih dan fit deep learning model di Keras, kita dapat menggunakannya untuk membuat prediksi pada instance data baru.

Ada beberapa kebingungan di kalangan pemula tentang bagaimana tepatnya melakukan ini. Sering terlihat pertanyaan seperti:

• Bagaimana cara membuat prediksi dengan model yang saya peroleh di Keras?

Dalam tutorial ini, kita akan menemukan bagaimana tepatnya kita dapat membuat prediksi klasifikasi dan regresi dengan model deep learning yang telah diperoleh dengan library Keras Python.

Setelah menyelesaikan tutorial ini, kita diharapkan bisa mengetahui tentang:

• Bagaimana memperoleh final model agar siap untuk digunakan untuk melakukan pediction.
• Bagaimana cara membuat class dan probability prediction untuk classification problem di Keras.
• Bagaimana cara melakukan regression prediction di Keras.

Finalisasi Model

Sebelum kita dapat membuat prediksi, kita harus me-train untuk memperoleh final model.

Kita mungkin telah men-train model menggunakan k-fold cross validation atau train/test split dari data yang ada. Ini dilakukan untuk memberi kita perkiraan kemampuan model pada data sampel, mis. ada yang data baru.

Model-model ini setelah memenuhi fungsi-nya, sekarang dapat dibuang.

Kita sekarang harus men-train final model menggunakan semua data yang tersedia. Kita dapat mempelajari lebih lanjut tentang cara me-train final model di:

• Keras: Cara Training Final Machine Learning Model

Classification Prediction

Masalah klasifikasi adalah masalah ketika model belajar memetakan antara fitur input dan fitur output yang merupakan label, seperti "spam" dan "not spam".

Bagi pemula dengan Keras ada baiknya membaca

• Keras: Develop Your First Neural Network in Python Step-By-Step

Di bawah ini adalah contoh finalized neural network model dalam Keras yang dikembangkan untuk masalah klasifikasi dua kelas (biner) sederhana.

# example of training a final classification model
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets.samples_generator import make_blobs
from sklearn.preprocessing import MinMaxScaler
# generate 2d classification dataset
X, y = make_blobs(n_samples=100, centers=2, n_features=2, random_state=1)
scalar = MinMaxScaler()
scalar.fit(X)
X = scalar.transform(X)
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='sigmoid'))
model.compile(loss='binary_crossentropy', optimizer='adam')
model.fit(X, y, epochs=200, verbose=0)

Setelah selesai, kita mungkin ingin menyimpan model ke file, mis. melalui API Keras. Setelah disimpan, kita dapat me-load model kapan saja dan menggunakannya untuk membuat prediksi. Untuk contohnya, lihat posting:

• Keras: Save and Load Your Keras Deep Learning Model

Untuk mempermudah, kita akan skip langkah ini sebagai contoh dalam tutorial ini.

Ada dua jenis prediksi klasifikasi yang ingin kita buat dengan model final; jenisnya adalah class prediction dan probability prediction.

Class Prediction

Prediksi kelas diberikan model final dan satu atau lebih instance data, memprediksi kelas untuk instance data.

Kita tidak tahu class yang akan dihasilkan untuk data baru. Itu sebabnya kita membutuhkan model tersebut.

Kita dapat memprediksi class untuk instance data baru menggunakan model klasifikasi final yang kita buat di Keras menggunakan fungsi predict_classes (). Perhatikan bahwa fungsi ini hanya tersedia pada model Sequential, bukan model yang dikembangkan menggunakan API fungsional.

Sebagai contoh, kita memiliki satu atau lebih contoh data dalam array yang disebut Xnew. Ini dapat diteruskan ke fungsi predict_classes () pada model kita untuk memprediksi nilai class untuk setiap instance dalam array.

Xnew = [[...], [...]]
ynew = model.predict_classes(Xnew)

Mari kita buat ini dengan contoh:

# example making new class predictions for a classification problem
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets.samples_generator import make_blobs
from sklearn.preprocessing import MinMaxScaler
# generate 2d classification dataset
X, y = make_blobs(n_samples=100, centers=2, n_features=2, random_state=1)
scalar = MinMaxScaler()
scalar.fit(X)
X = scalar.transform(X)
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='sigmoid'))
model.compile(loss='binary_crossentropy', optimizer='adam')
model.fit(X, y, epochs=500, verbose=0)
# new instances where we do not know the answer
Xnew, _ = make_blobs(n_samples=3, centers=2, n_features=2, random_state=1)
Xnew = scalar.transform(Xnew)
# make a prediction
ynew = model.predict_classes(Xnew)
# show the inputs and predicted outputs
for i in range(len(Xnew)):
	print("X=%s, Predicted=%s" % (Xnew[i], ynew[i]))

Menjalankan contoh untuk memprediksi class untuk tiga contoh data baru, lalu mem-print data dan hasil prediksi-nya.

X=[0.89337759 0.65864154], Predicted=[0]
X=[0.29097707 0.12978982], Predicted=[1]
X=[0.78082614 0.75391697], Predicted=[0]

Jika kita hanya memiliki satu instance data baru, kita bisa memberikan ini sebagai instance yang dibungkus dalam array ke fungsi predict_classes (); sebagai contoh:

# example making new class prediction for a classification problem
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets.samples_generator import make_blobs
from sklearn.preprocessing import MinMaxScaler
from numpy import array
# generate 2d classification dataset
X, y = make_blobs(n_samples=100, centers=2, n_features=2, random_state=1)
scalar = MinMaxScaler()
scalar.fit(X)
X = scalar.transform(X)
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='sigmoid'))
model.compile(loss='binary_crossentropy', optimizer='adam')
model.fit(X, y, epochs=500, verbose=0)
# new instance where we do not know the answer
Xnew = array(0.89337759, 0.65864154)
# make a prediction
ynew = model.predict_classes(Xnew)
# show the inputs and predicted outputs
print("X=%s, Predicted=%s" % (Xnew[0], ynew[0]))

Menjalankan contoh mem-print instance tunggal dan mem-prediksi class.

X=[0.89337759 0.65864154], Predicted=[0]

Catatan tentang Class Label

Catatan bahwa saat kita menyiapkan data, kita akan memetakan nilai class dari domain yang kita gunakan (seperti string) ke nilai integer. Kita mungkin telah menggunakan LabelEncoder.

LabelEncoder ini dapat digunakan untuk mengonversi bilangan integer kembali ke nilai string melalui fungsi inverse_transform ().

Untuk alasan ini, kita mungkin ingin menyimpan (pickle) LabelEncoder yang digunakan untuk meng-encode nilai y yang kita gunakan saat melakukan fitting final model kita.

Probability Prediction

Another type of prediction you may wish to make is the probability of the data instance belonging to each class.

This is called a probability prediction where, given a new instance, the model returns the probability for each outcome class as a value between 0 and 1.

You can make these types of predictions in Keras by calling the predict_proba() function; for example:

Xnew = [[...], [...]]
ynew = model.predict_proba(Xnew)

In the case of a two-class (binary) classification problem, the sigmoid activation function is often used in the output layer. The predicted probability is taken as the likelihood of the observation belonging to class 1, or inverted (1 – probability) to give the probability for class 0.

In the case of a multi-class classification problem, the softmax activation function is often used on the output layer and the likelihood of the observation for each class is returned as a vector.

The example below makes a probability prediction for each example in the Xnew array of data instance.

# example making new probability predictions for a classification problem
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets.samples_generator import make_blobs
from sklearn.preprocessing import MinMaxScaler
# generate 2d classification dataset
X, y = make_blobs(n_samples=100, centers=2, n_features=2, random_state=1)
scalar = MinMaxScaler()
scalar.fit(X)
X = scalar.transform(X)
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='sigmoid'))
model.compile(loss='binary_crossentropy', optimizer='adam')
model.fit(X, y, epochs=500, verbose=0)
# new instances where we do not know the answer
Xnew, _ = make_blobs(n_samples=3, centers=2, n_features=2, random_state=1)
Xnew = scalar.transform(Xnew)
# make a prediction
ynew = model.predict_proba(Xnew)
# show the inputs and predicted outputs
for i in range(len(Xnew)):
	print("X=%s, Predicted=%s" % (Xnew[i], ynew[i]))

Running the instance makes the probability predictions and then prints the input data instance and the probability of each instance belonging to class 1.

X=[0.89337759 0.65864154], Predicted=[0.0087348]
X=[0.29097707 0.12978982], Predicted=[0.82020265]
X=[0.78082614 0.75391697], Predicted=[0.00693122]

This can be helpful in your application if you want to present the probabilities to the user for expert interpretation. 3. Regression Predictions

Regression is a supervised learning problem where given input examples, the model learns a mapping to suitable output quantities, such as “0.1” and “0.2”, etc.

Below is an example of a finalized Keras model for regression.

# example of training a final regression model
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets import make_regression
from sklearn.preprocessing import MinMaxScaler
# generate regression dataset
X, y = make_regression(n_samples=100, n_features=2, noise=0.1, random_state=1)
scalarX, scalarY = MinMaxScaler(), MinMaxScaler()
scalarX.fit(X)
scalarY.fit(y.reshape(100,1))
X = scalarX.transform(X)
y = scalarY.transform(y.reshape(100,1))
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='linear'))
model.compile(loss='mse', optimizer='adam')
model.fit(X, y, epochs=1000, verbose=0)

We can predict quantities with the finalized regression model by calling the predict() function on the finalized model.

The predict() function takes an array of one or more data instances.

The example below demonstrates how to make regression predictions on multiple data instances with an unknown expected outcome.

# example of making predictions for a regression problem
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets import make_regression
from sklearn.preprocessing import MinMaxScaler
# generate regression dataset
X, y = make_regression(n_samples=100, n_features=2, noise=0.1, random_state=1)
scalarX, scalarY = MinMaxScaler(), MinMaxScaler()
scalarX.fit(X)
scalarY.fit(y.reshape(100,1))
X = scalarX.transform(X)
y = scalarY.transform(y.reshape(100,1))
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='linear'))
model.compile(loss='mse', optimizer='adam')
model.fit(X, y, epochs=1000, verbose=0)
# new instances where we do not know the answer
Xnew, a = make_regression(n_samples=3, n_features=2, noise=0.1, random_state=1)
Xnew = scalarX.transform(Xnew)
# make a prediction
ynew = model.predict(Xnew)
# show the inputs and predicted outputs
for i in range(len(Xnew)):
	print("X=%s, Predicted=%s" % (Xnew[i], ynew[i]))

Running the example makes multiple predictions, then prints the inputs and predictions side by side for review.

X=[0.29466096 0.30317302], Predicted=[0.17097184]
X=[0.39445118 0.79390858], Predicted=[0.7475489]
X=[0.02884127 0.6208843 ], Predicted=[0.43370453]

The same function can be used to make a prediction for a single data instance, as long as it is suitably wrapped in a surrounding list or array.

For example:

# example of making predictions for a regression problem
from keras.models import Sequential
from keras.layers import Dense
from sklearn.datasets import make_regression
from sklearn.preprocessing import MinMaxScaler
from numpy import array
# generate regression dataset
X, y = make_regression(n_samples=100, n_features=2, noise=0.1, random_state=1)
scalarX, scalarY = MinMaxScaler(), MinMaxScaler()
scalarX.fit(X)
scalarY.fit(y.reshape(100,1))
X = scalarX.transform(X)
y = scalarY.transform(y.reshape(100,1))
# define and fit the final model
model = Sequential()
model.add(Dense(4, input_dim=2, activation='relu'))
model.add(Dense(4, activation='relu'))
model.add(Dense(1, activation='linear'))
model.compile(loss='mse', optimizer='adam')
model.fit(X, y, epochs=1000, verbose=0)
# new instance where we do not know the answer
Xnew = array(0.29466096, 0.30317302)
# make a prediction
ynew = model.predict(Xnew)
# show the inputs and predicted outputs
print("X=%s, Predicted=%s" % (Xnew[0], ynew[0]))

Running the example makes a single prediction and prints the data instance and prediction for review.

X=[0.29466096 0.30317302], Predicted=[0.17333156]

Further Reading

This section provides more resources on the topic if you are looking to go deeper.

   How to Train a Final Machine Learning Model
   Save and Load Your Keras Deep Learning Models
   Develop Your First Neural Network in Python With Keras Step-By-Step
   The 5 Step Life-Cycle for Long Short-Term Memory Models in Keras
   How to Make Predictions with Long Short-Term Memory Models in Keras

Summary

In this tutorial, you discovered how you can make classification and regression predictions with a finalized deep learning model with the Keras Python library.

Specifically, you learned:

• How to finalize a model in order to make it ready for making predictions.
• How to make class and probability predictions for classification problems in Keras.
• How to make regression predictions in in Keras.

Do you have any questions? Ask your questions in the comments below and I will do my best to answer.

Referensi

• https://machinelearningmastery.com/how-to-make-classification-and-regression-predictions-for-deep-learning-models-in-keras/

Pranala Menarik

• Keras
• Python