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[인프런] Google 공인! 텐서플로(TensorFlow) 딥러닝 개발자 자격증 취득 - 후기 구경가기

12 분 소요

BBC 뉴스 아티클 묶음 데이터셋인 bbc-text.csv 파일을 활용하여 TensorFlow 의 Tokenizer로 단어 사전을 만들고 자연어 처리 모델 학습을 위한 데이터 전처리를 진행해 보겠습니다. bbc-text.csv 파일을 pandas로 읽어와서 데이터프레임 변환 후 라벨 인코딩을 포함한 간단한 전처리를 다룹니다.

문장 데이터(text) 전처리에서는 토크나이저 생성, 단어 사전 생성, 불용어(stopwords) 처리, 시퀀스 변환 등을 다룹니다.

모델링에서는 Embedding layerBidirectional LSTM으로 BBC 뉴스 아티클의 뉴스 카테고리 분류기를 생성하겠습니다.

(본 예제는 텐서플로 자격 인증 시험(TensorFlow Developers Certificate)의 기출 문제 중 하나를 다뤄 본 튜토리얼입니다.)

Dataset Reference

About this file

Source data from public data set on BBC news articles:
D. Greene and P. Cunningham. "Practical Solutions to the Problem of Diagonal Dominance in Kernel Document Clustering", Proc. ICML 2006. [PDF] [BibTeX].

http://mlg.ucd.ie/datasets/bbc.html

Cleaned up version exported to https://storage.googleapis.com/dataset-uploader/bbc/bbc-text.csv

필요한 모듈 import

import tensorflow as tf
import numpy as np
import urllib
import pandas as pd

from tensorflow.keras.preprocessing.text import Tokenizer
from tensorflow.keras.preprocessing.sequence import pad_sequences

from tensorflow.keras.models import Sequential
from tensorflow.keras.layers import Embedding, LSTM, Dense, Bidirectional
from tensorflow.keras.models import Sequential
from tensorflow.keras.callbacks import ModelCheckpoint

데이터셋 다운로드

url = 'https://storage.googleapis.com/download.tensorflow.org/data/bbc-text.csv'
urllib.request.urlretrieve(url, 'bbc-text.csv')

다운로드 받은 bbc-text.csv 파일을 읽어서 df 변수에 로드 합니다.

df = pd.read_csv('bbc-text.csv')
df
category text
0 tech tv future in the hands of viewers with home th...
1 business worldcom boss left books alone former worldc...
2 sport tigers wary of farrell gamble leicester say ...
3 sport yeading face newcastle in fa cup premiership s...
4 entertainment ocean s twelve raids box office ocean s twelve...
... ... ...
2220 business cars pull down us retail figures us retail sal...
2221 politics kilroy unveils immigration policy ex-chatshow ...
2222 entertainment rem announce new glasgow concert us band rem h...
2223 politics how political squabbles snowball it s become c...
2224 sport souness delight at euro progress boss graeme s...

2225 rows × 2 columns

Label 값 확인

category 종류 확인

df['category'].value_counts()
sport            511
business         510
politics         417
tech             401
entertainment    386
Name: category, dtype: int64

위의 value_counts() 함수로 label의 value는 sport, business, politics, tech, entertainment` 이렇게 5가지의 종류가 존재합니다.

하지만, TensorFlow Certificate 시험에서는 아래와 같은 가이드라인을 줍니다.


PLEASE NOTE -- WHILE THERE ARE 5 CATEGORIES, THEY ARE NUMBERED 1 THROUGH 5 IN THE DATASET

SO IF YOU ONE-HOT ENCODE THEM, THEY WILL END UP WITH 6 VALUES, SO THE OUTPUT LAYER HERE

SHOULD ALWAYS HAVE 6 NEURONS AS BELOW. MAKE SURE WHEN YOU ENCODE YOUR LABELS THAT YOU USE

THE SAME FORMAT, OR THE TESTS WILL FAIL

0 = UNUSED

1 = SPORT

2 = BUSINESS

3 = POLITICS

4 = TECH

5 = ENTERTAINMENT

즉, 5개의 카테고리가 존재하는 것은 맞지만 0번 label 에는 UNUSED 항목을 남겨 놓고, 1~5번 라벨에 맵핑되는 카테고리를 규정하고 있습니다.

반드시 위의 번호에 맞게 라벨 인코딩을 해줘야 채점서버에서 올바르게 채점을 진행할 수 있기에, 라벨 인코딩시 위의 규정에 따라 인코딩을 진행하여야 합니다.

# category encoding map
m = {
    'unused': 0, 
    'sport': 1, 
    'business': 2, 
    'politics': 3, 
    'tech': 4, 
    'entertainment': 5
}

# map 함수로 인코딩 변환
df['category'] = df['category'].map(m)
df['category'].value_counts()
1    511
2    510
3    417
4    401
5    386
Name: category, dtype: int64

0번 라벨 값은 없었기 때문에 0번을 제외한 1~5번까지 올바르게 출력됨을 확인할 수 있습니다.

# hyperparameter settings
vocab_size = 1000
embedding_dim = 16
max_length = 120
trunc_type='post'
padding_type='post'
oov_tok = "<OOV>"
training_size = 2000

# 불용어 정의
stopwords = [ "a", "about", "above", "after", "again", "against", "all", "am", "an", "and", "any", "are", "as", "at", "be", "because", "been", "before", "being", "below", "between", "both", "but", "by", "could", "did", "do", "does", "doing", "down", "during", "each", "few", "for", "from", "further", "had", "has", "have", "having", "he", "he'd", "he'll", "he's", "her", "here", "here's", "hers", "herself", "him", "himself", "his", "how", "how's", "i", "i'd", "i'll", "i'm", "i've", "if", "in", "into", "is", "it", "it's", "its", "itself", "let's", "me", "more", "most", "my", "myself", "nor", "of", "on", "once", "only", "or", "other", "ought", "our", "ours", "ourselves", "out", "over", "own", "same", "she", "she'd", "she'll", "she's", "should", "so", "some", "such", "than", "that", "that's", "the", "their", "theirs", "them", "themselves", "then", "there", "there's", "these", "they", "they'd", "they'll", "they're", "they've", "this", "those", "through", "to", "too", "under", "until", "up", "very", "was", "we", "we'd", "we'll", "we're", "we've", "were", "what", "what's", "when", "when's", "where", "where's", "which", "while", "who", "who's", "whom", "why", "why's", "with", "would", "you", "you'd", "you'll", "you're", "you've", "your", "yours", "yourself", "yourselves" ]

아래에서 sentenceslabels 변수에 textcategory 컬럼을 리스트 변환하여 담은 뒤 간단한 전처리를 수행합니다.

# sentence 와 labals를 분리 합니다.
sentences = df['text'].tolist()
labels = df['category'].tolist()

cleaned_sentences 라는 빈 리스트를 생성한 뒤, 각 문장에서 불용어를 제외한 뒤 다시 쪼개진 단어를 합쳐서 추가합니다.

불용어(stopwords) 란?

문장 내에서 빈번하게 발생하여 의미를 부여하기 어려운 단어들을 의미합니다.

‘a’, ‘the’, ‘in’ 같은 단어들은 모든 구문에 빈번히 등장하지만 의미가 없습니다.

특히 불용어는 자연어 처리에 있어 효율성을 감소시키기 때문에 가능하다면 제거하는 것이 좋습니다.

cleaned_sentences = []

for sentence in sentences:
    # list comprehension
    cleaned = [word for word in sentence.split() if word not in stopwords]
    cleaned_sentences.append(' '.join(cleaned))
    
# 불용어 처리 전
print(f'[불용어 처리 전] {sentences[0][:100]}')

# 불용어 처리 후
print(f'[불용어 처리 후] {cleaned_sentences[0][:100]}')
[불용어 처리 전] tv future in the hands of viewers with home theatre systems  plasma high-definition tvs  and digital
[불용어 처리 후] tv future hands viewers home theatre systems plasma high-definition tvs digital video recorders movi

train / validation 셋으로 나눕니다.

train_sentences = cleaned_sentences[:training_size]
validation_sentences = cleaned_sentences[training_size:]

train_labels = labels[:training_size]
validation_labels = labels[training_size:]

토크나이저 정의

tensorflow.keras.preprocessing.text.Tokenizer를 생성합니다.

  • num_words: 몇 개의 단어 사전을 활용할지 지정합니다.

  • oov_token: Out of Vocab 토큰을 지정합니다. 보통 겹치지 않는(일반적으로 사용하지 않은 특수 문자 조합으로..) 문자열로 지정합니다.

# vocab_size = 1000
# oov_token 지정
tokenizer = Tokenizer(num_words=vocab_size, oov_token=oov_tok)

# 단어 사전을 생성합니다.
tokenizer.fit_on_texts(train_sentences)
# 문장을 시퀀스로 변환합니다.
train_sequences = tokenizer.texts_to_sequences(train_sentences)
validation_sequences = tokenizer.texts_to_sequences(validation_sentences)
# padding 처리를 수행하여 한 문장의 길이를 맞춥니다.
# maxlen은 120 단어로 지정하였습니다.
train_padded = pad_sequences(train_sequences, padding=padding_type, maxlen=max_length, truncating=trunc_type)
validation_padded = pad_sequences(validation_sequences, padding=padding_type, maxlen=max_length, truncating=trunc_type)
# 결과물 shape 확인
train_padded.shape
(2000, 120)
# 0번째 index 출력
train_padded[0]
array([101, 176,   1,   1,  54,   1, 782,   1,  95,   1,   1, 143, 188,
         1,   1,   1,   1,  47,   9, 934, 101,   4,   1, 371,  87,  23,
        17, 144,   1,   1,   1, 588, 454,   1,  71,   1,   1,   1,  10,
       834,   4, 800,  12, 869,   1,  11, 643,   1,   1, 412,   4,   1,
         1, 775,  54, 559,   1,   1,   1, 148, 303, 128,   1, 801,   1,
         1, 599,  12,   1,   1, 834,   1, 143, 354, 188,   1,   1,   1,
        42,  68,   1,  31,  11,   2,   1,  22,   2,   1, 138, 439,   9,
       146,   1,  80,   1, 471,   1, 101,   1,  86,   1,  93,   1,  61,
         1, 101,   8,   1, 644,  95,   1, 101,   1, 139, 164, 469,  11,
         1,  46,  56], dtype=int32)

1로 마킹되어 있는 단어들이 많이 보입니다. 1 로 마킹된 단어들은 OOV 토큰입니다.

# label을 numpy array 로 변환합니다.
train_labels = np.array(train_labels)
validation_labels = np.array(validation_labels)

모델

# model 생성
model = Sequential([
    Embedding(vocab_size, embedding_dim, input_length=max_length),
    Bidirectional(LSTM(64, return_sequences=True)),
    Bidirectional(LSTM(64)),
    Dense(32, activation='relu'),
    Dense(16, activation='relu'),
    Dense(6, activation='softmax')
])

컴파일시 losssparse_categorical_crossentropy를 지정하였습니다 (별도의 원핫인코딩을 수행하지 않았기 때문).

# model compile
model.compile(optimizer='adam', loss='sparse_categorical_crossentropy', metrics=['acc'])

체크포인트를 생성합니다. val_loss 기준으로 가장 최저점의 체크포인트를 학습이 완료된 뒤 로드합니다.

checkpoint_path = 'bbc_checkpoint.ckpt'
checkpoint = ModelCheckpoint(checkpoint_path, 
                             save_weights_only=True, 
                             save_best_only=True, 
                             monitor='val_loss',
                             verbose=1)

모델을 학습합니다. epochs를 충분히 주어 원하는 val_loss, val_acc에 도달할 때까지 학습합니다.

history = model.fit(train_padded, train_labels,
                    validation_data=(validation_padded, validation_labels),
                    callbacks=[checkpoint],
                    epochs=30)
Epoch 1/30
61/63 [============================>.] - ETA: 0s - loss: 1.6741 - acc: 0.2039
Epoch 00001: val_loss improved from inf to 1.63404, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 5s 33ms/step - loss: 1.6717 - acc: 0.2075 - val_loss: 1.6340 - val_acc: 0.1911
Epoch 2/30
61/63 [============================>.] - ETA: 0s - loss: 1.4633 - acc: 0.3294
Epoch 00002: val_loss improved from 1.63404 to 1.37903, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 1.4598 - acc: 0.3315 - val_loss: 1.3790 - val_acc: 0.3333
Epoch 3/30
61/63 [============================>.] - ETA: 0s - loss: 1.2494 - acc: 0.4252
Epoch 00003: val_loss improved from 1.37903 to 1.16279, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 1.2487 - acc: 0.4250 - val_loss: 1.1628 - val_acc: 0.4444
Epoch 4/30
61/63 [============================>.] - ETA: 0s - loss: 1.0220 - acc: 0.5277
Epoch 00004: val_loss improved from 1.16279 to 1.02034, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 1.0172 - acc: 0.5305 - val_loss: 1.0203 - val_acc: 0.5111
Epoch 5/30
61/63 [============================>.] - ETA: 0s - loss: 0.9038 - acc: 0.5758
Epoch 00005: val_loss did not improve from 1.02034
63/63 [==============================] - 1s 20ms/step - loss: 0.8989 - acc: 0.5805 - val_loss: 1.0432 - val_acc: 0.5422
Epoch 6/30
62/63 [============================>.] - ETA: 0s - loss: 0.7046 - acc: 0.7122
Epoch 00006: val_loss improved from 1.02034 to 0.72509, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 0.7021 - acc: 0.7140 - val_loss: 0.7251 - val_acc: 0.6756
Epoch 7/30
61/63 [============================>.] - ETA: 0s - loss: 0.5501 - acc: 0.7859
Epoch 00007: val_loss improved from 0.72509 to 0.70795, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 0.5455 - acc: 0.7890 - val_loss: 0.7079 - val_acc: 0.6711
Epoch 8/30
62/63 [============================>.] - ETA: 0s - loss: 0.3505 - acc: 0.8720
Epoch 00008: val_loss improved from 0.70795 to 0.45064, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 0.3484 - acc: 0.8730 - val_loss: 0.4506 - val_acc: 0.8311
Epoch 9/30
61/63 [============================>.] - ETA: 0s - loss: 0.2467 - acc: 0.9180
Epoch 00009: val_loss did not improve from 0.45064
63/63 [==============================] - 1s 20ms/step - loss: 0.2440 - acc: 0.9185 - val_loss: 0.4995 - val_acc: 0.8533
Epoch 10/30
61/63 [============================>.] - ETA: 0s - loss: 0.2481 - acc: 0.9191
Epoch 00010: val_loss improved from 0.45064 to 0.43606, saving model to bbc_checkpoint.ckpt
63/63 [==============================] - 1s 20ms/step - loss: 0.2450 - acc: 0.9200 - val_loss: 0.4361 - val_acc: 0.8844
Epoch 11/30
62/63 [============================>.] - ETA: 0s - loss: 0.1306 - acc: 0.9637
Epoch 00011: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.1298 - acc: 0.9640 - val_loss: 0.5338 - val_acc: 0.8667
Epoch 12/30
61/63 [============================>.] - ETA: 0s - loss: 0.1060 - acc: 0.9708
Epoch 00012: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.1040 - acc: 0.9715 - val_loss: 0.4474 - val_acc: 0.8844
Epoch 13/30
61/63 [============================>.] - ETA: 0s - loss: 0.1686 - acc: 0.9426
Epoch 00013: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.1688 - acc: 0.9425 - val_loss: 0.7164 - val_acc: 0.8044
Epoch 14/30
62/63 [============================>.] - ETA: 0s - loss: 0.1827 - acc: 0.9471
Epoch 00014: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.1816 - acc: 0.9475 - val_loss: 0.5031 - val_acc: 0.8667
Epoch 15/30
61/63 [============================>.] - ETA: 0s - loss: 0.0930 - acc: 0.9708
Epoch 00015: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0920 - acc: 0.9710 - val_loss: 0.5199 - val_acc: 0.8622
Epoch 16/30
61/63 [============================>.] - ETA: 0s - loss: 0.0404 - acc: 0.9898
Epoch 00016: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0442 - acc: 0.9890 - val_loss: 0.4765 - val_acc: 0.9022
Epoch 17/30
61/63 [============================>.] - ETA: 0s - loss: 0.0504 - acc: 0.9836
Epoch 00017: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0494 - acc: 0.9840 - val_loss: 0.5070 - val_acc: 0.8889
Epoch 18/30
62/63 [============================>.] - ETA: 0s - loss: 0.0448 - acc: 0.9854
Epoch 00018: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0444 - acc: 0.9855 - val_loss: 0.5073 - val_acc: 0.8844
Epoch 19/30
61/63 [============================>.] - ETA: 0s - loss: 0.0404 - acc: 0.9867
Epoch 00019: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0405 - acc: 0.9865 - val_loss: 0.7229 - val_acc: 0.8578
Epoch 20/30
61/63 [============================>.] - ETA: 0s - loss: 0.0649 - acc: 0.9790
Epoch 00020: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0636 - acc: 0.9795 - val_loss: 0.5101 - val_acc: 0.9022
Epoch 21/30
61/63 [============================>.] - ETA: 0s - loss: 0.0333 - acc: 0.9898
Epoch 00021: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0328 - acc: 0.9900 - val_loss: 0.6735 - val_acc: 0.8844
Epoch 22/30
62/63 [============================>.] - ETA: 0s - loss: 0.0218 - acc: 0.9934
Epoch 00022: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0217 - acc: 0.9935 - val_loss: 0.5494 - val_acc: 0.9067
Epoch 23/30
61/63 [============================>.] - ETA: 0s - loss: 0.0375 - acc: 0.9887
Epoch 00023: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0378 - acc: 0.9885 - val_loss: 0.5719 - val_acc: 0.9111
Epoch 24/30
61/63 [============================>.] - ETA: 0s - loss: 0.0800 - acc: 0.9734
Epoch 00024: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0804 - acc: 0.9730 - val_loss: 0.6355 - val_acc: 0.8844
Epoch 25/30
61/63 [============================>.] - ETA: 0s - loss: 0.0606 - acc: 0.9872
Epoch 00025: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0592 - acc: 0.9875 - val_loss: 0.5286 - val_acc: 0.9067
Epoch 26/30
61/63 [============================>.] - ETA: 0s - loss: 0.0158 - acc: 0.9954
Epoch 00026: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0162 - acc: 0.9950 - val_loss: 0.5403 - val_acc: 0.9022
Epoch 27/30
61/63 [============================>.] - ETA: 0s - loss: 0.0128 - acc: 0.9974
Epoch 00027: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0125 - acc: 0.9975 - val_loss: 0.5612 - val_acc: 0.9022
Epoch 28/30
61/63 [============================>.] - ETA: 0s - loss: 0.0074 - acc: 0.9990
Epoch 00028: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 20ms/step - loss: 0.0073 - acc: 0.9990 - val_loss: 0.5918 - val_acc: 0.9022
Epoch 29/30
62/63 [============================>.] - ETA: 0s - loss: 0.0087 - acc: 0.9990
Epoch 00029: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 19ms/step - loss: 0.0087 - acc: 0.9990 - val_loss: 0.6322 - val_acc: 0.8978
Epoch 30/30
62/63 [============================>.] - ETA: 0s - loss: 0.0070 - acc: 0.9985
Epoch 00030: val_loss did not improve from 0.43606
63/63 [==============================] - 1s 19ms/step - loss: 0.0070 - acc: 0.9985 - val_loss: 0.6204 - val_acc: 0.9022

학습이 완료된 뒤 저장한 체크포인트를 load 합니다.

# checkpoint 로드
model.load_weights(checkpoint_path)

validation_paddedvalidation_labels로 최종 성능평가를 수행합니다.

# 모델 평가
model.evaluate(validation_padded, validation_labels)
8/8 [==============================] - 0s 8ms/step - loss: 0.4361 - acc: 0.8844
[0.43605977296829224, 0.8844444155693054]

학습 결과 시각화

import matplotlib.pyplot as plt


fig, axes = plt.subplots(1, 2)
fig.set_size_inches(10, 4)
axes[0].plot(history.history['loss'], color='#5A98BF', alpha=0.5, linestyle=':', label='loss')
axes[0].plot(history.history['val_loss'], color='#5A98BF', linestyle='-', label='val_loss')
axes[0].set_xlabel('Epochs', fontsize=10)
axes[0].set_ylabel('Loss', fontsize=10)
axes[0].set_title('Losses')
axes[0].tick_params(axis='both', which='major', labelsize=8)
axes[0].tick_params(axis='both', which='minor', labelsize=6)
axes[0].legend()

axes[1].plot(history.history['acc'], color='#F2294E', alpha=0.3, linestyle=':', label='acc')
axes[1].plot(history.history['val_acc'], color='#F2294E', linestyle='-', label='val_acc')
axes[1].set_xlabel('Epochs')
axes[1].set_ylabel('Accuracy')
axes[1].set_title('Accuracy')
axes[1].tick_params(axis='both', which='major', labelsize=8)
axes[1].tick_params(axis='both', which='minor', labelsize=6)
axes[1].legend()

plt.show()

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