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I am using PASCAL VOC 2012 dataset for image classification. A few images have multiple labels where as a few of them have single labels as shown below.
0 2007_000027.jpg {'person'}
1 2007_000032.jpg {'aeroplane', 'person'}
2 2007_000033.jpg {'aeroplane'}
3 2007_000039.jpg {'tvmonitor'}
4 2007_000042.jpg {'train'}
I want to do one-hot encoding of these labels to train the model. However, I couldn't use keras.utils.to_categorical, as these labels are not integers and pandas.get_dummies is not giving me the results as expected. get_dummies is giving different categories as below, i.e. it is taking each unique combination of labels as one category.
{'aeroplane', 'bus', 'car'} {'aeroplane', 'bus'} {'tvmonitor', 'sofa'} {'tvmonitor'} ...
What is the best way to one-hot encode these labels as we don't have specific number of labels for each image.
757
Multi-Class Classification Scores from the last layer are passed through a softmax layer. The softmax layer converts the score into probability values. At last, data is classified into a corresponding class, that has the highest probability value.
There are two main methods for tackling a multi-label classification problem: problem transformation methods and algorithm adaptation methods. Problem transformation methods transform the multi-label problem into a set of binary classification problems, which can then be handled using single-class classifiers.
Each node in the output layer must use the sigmoid activation. This will predict a probability of class membership for the label, a value between 0 and 1. Finally, the model must be fit with the binary cross-entropy loss function.
The MultiLabelBinarizer class allow to do one-hot encoding on multilabel sets, like you have in column b:
print (df)
a b
0 2007_000027.jpg {'person'}
1 2007_000032.jpg {'aeroplane', 'person'}
2 2007_000033.jpg {'aeroplane'}
3 2007_000039.jpg {'tvmonitor'}
4 2007_000042.jpg {'train'}
from sklearn.preprocessing import MultiLabelBinarizer
mlb = MultiLabelBinarizer()
df = pd.DataFrame(mlb.fit_transform(df['b']),columns=mlb.classes_)
print (df)
aeroplane person train tvmonitor
0 0 1 0 0
1 1 1 0 0
2 1 0 0 0
3 0 0 0 1
4 0 0 1 0
Or Series.str.join with Series.str.get_dummies, but it should be slower in large DataFrame:
df = df['b'].str.join('|').str.get_dummies()
print (df)
aeroplane person train tvmonitor
0 0 1 0 0
1 1 1 0 0
2 1 0 0 0
3 0 0 0 1
4 0 0 1 0
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