PyTorch Lecture 08: PyTorch DataLoader

# References
# https://github.com/yunjey/pytorch-tutorial/blob/master/tutorials/01-basics/pytorch_basics/main.py
# http://pytorch.org/tutorials/beginner/data_loading_tutorial.html#dataset-class
import torch
import numpy as np
from torch.autograd import Variable
from torch.utils.data import Dataset, DataLoader


class DiabetesDataset(Dataset):
    """ Diabetes dataset."""

    # Initialize your data, download, etc.
    def __init__(self):
        xy = np.loadtxt('./data/diabetes.csv.gz',
                        delimiter=',', dtype=np.float32)
        self.len = xy.shape[0]
        self.x_data = torch.from_numpy(xy[:, 0:-1])
        self.y_data = torch.from_numpy(xy[:, [-1]])

    def __getitem__(self, index):
        return self.x_data[index], self.y_data[index]

    def __len__(self):
        return self.len


dataset = DiabetesDataset()
train_loader = DataLoader(dataset=dataset,
                          batch_size=32,
                          shuffle=True,
                          num_workers=2)


class Model(torch.nn.Module):

    def __init__(self):
        """
        In the constructor we instantiate two nn.Linear module
        """
        super(Model, self).__init__()
        self.l1 = torch.nn.Linear(8, 6)
        self.l2 = torch.nn.Linear(6, 4)
        self.l3 = torch.nn.Linear(4, 1)

        self.sigmoid = torch.nn.Sigmoid()

    def forward(self, x):
        """
        In the forward function we accept a Variable of input data and we must return
        a Variable of output data. We can use Modules defined in the constructor as
        well as arbitrary operators on Variables.
        """
        out1 = self.sigmoid(self.l1(x))
        out2 = self.sigmoid(self.l2(out1))
        y_pred = self.sigmoid(self.l3(out2))
        return y_pred

if __name__ == '__main__':
    # our model
    model = Model()

    # Construct our loss function and an Optimizer. The call to model.parameters()
    # in the SGD constructor will contain the learnable parameters of the two
    # nn.Linear modules which are members of the model.
    criterion = torch.nn.BCELoss(size_average=True)
    optimizer = torch.optim.SGD(model.parameters(), lr=0.1)

    # Training loop
    for epoch in range(2):
        for i, data in enumerate(train_loader, 0):
            # get the inputs
            inputs, labels = data

            # wrap them in Variable
            inputs, labels = Variable(inputs), Variable(labels)

            # Forward pass: Compute predicted y by passing x to the model
            y_pred = model(inputs)

            # Compute and print loss
            loss = criterion(y_pred, labels)
            print(epoch, i, loss.data[0])

            # Zero gradients, perform a backward pass, and update the weights.
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()