pytorch forum code for loocv

from __future__ import print_function, division

import torch
from torch.autograd import Variable
from sklearn.metrics import accuracy_score
from sklearn.metrics import confusion_matrix
import torch
import torch.nn as nn
import torch.optim as optim
from torch.optim import lr_scheduler
import numpy as np
import torchvision
from torchvision import datasets, models, transforms
import matplotlib.pyplot as plt
import time
import os
import copy

import torch.utils.data as data_utils
from torch.utils import data

torch.manual_seed(2809)


def train_model(model, criterion, optimizer, scheduler,
                train_input, train_label, num_epochs=25):
    since = time.time()
    model.train()  # Set model to training mode
    for epoch in range(num_epochs):
        print('Epoch {}/{}'.format(epoch, num_epochs - 1))
        print('-' * 10)

        scheduler.step()

        running_loss = 0.0
        running_corrects = 0

        # Iterate over data.
        train_input = train_input.to(device)
        train_label = train_label.to(device)

        # zero the parameter gradients
        optimizer.zero_grad()

        output = model(train_input)
        _, pred = torch.max(output, 1)
        loss = criterion(output, train_label)
        loss.backward()
        optimizer.step()

        # statistics
        running_loss += loss.item() * train_input.size(0)
        running_corrects += torch.sum(pred == train_label.data)

        epoch_loss = running_loss / dataset_size['train']
        epoch_acc = running_corrects.double() / dataset_size['train']

        print('train Loss: {:.4f} Acc: {:.4f}'.format(epoch_loss, epoch_acc))

        print()

    time_elapsed = time.time() - since
    print('Training complete in {:.0f}m {:.0f}s'.format(
        time_elapsed // 60, time_elapsed % 60))

    return model


data_transforms = {
    'train': transforms.Compose([
        transforms.RandomResizedCrop(224),
        transforms.RandomHorizontalFlip(),
        transforms.RandomRotation(20),
        transforms.ToTensor(),
        transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])
    ]),
    'test': transforms.Compose([
        transforms.Resize(224),
        transforms.ToTensor(),
        transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])
    ])
}


data_dir = "test_images"
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")

model_ft = models.resnet50(pretrained=True)
num_ftrs = model_ft.fc.in_features
model_ft.fc = nn.Linear(num_ftrs, 2)
model_ft = model_ft.to(device)

# Save a clone of initial model to restore later
initial_model = copy.deepcopy(model_ft)

criterion = nn.CrossEntropyLoss()

# Observe that all parameters are being optimized
optimizer_ft = optim.SGD(model_ft.parameters(), lr=0.001, momentum=0.9)

# Decay LR by a factor of 0.1 every 7 epochs
exp_lr_scheduler = lr_scheduler.StepLR(optimizer_ft, step_size=7, gamma=0.1)

#model_ft = model_ft.cuda()
nb_samples = 10
nb_classes = 2

image_datasets = {x: datasets.ImageFolder(os.path.join(data_dir, x),
                                          data_transforms[x])
                  for x in ['train']}

dataset_size = {x: len(image_datasets[x]) for x in ['train']}
class_names = image_datasets['train'].classes

# LOOCV
loocv_preds = []
loocv_targets = []
for idx in range(nb_samples):

    print('Using sample {} as test data'.format(idx))

    print('Resetting model')
    model_ft = copy.deepcopy(initial_model)

    # Get all indices and remove test sample
    train_indices = list(range(len(image_datasets['train'])))
    del train_indices[idx]

    # Create new sampler
    sampler = data.SubsetRandomSampler(train_indices)
    dataloader = data.DataLoader(
        image_datasets['train'],
        num_workers=2,
        batch_size=1,
        sampler=sampler
    )

    # Train model
    for batch_idx, (sample, target) in enumerate(dataloader):
        print('Batch {}'.format(batch_idx))
        model_ft = train_model(model_ft, criterion, optimizer_ft, exp_lr_scheduler, sample, target, num_epochs=1)

    # Test on LOO sample
    model_ft.eval()
    test_data, test_target = image_datasets['train'][idx]
    # Apply test preprocessing on data
    print(type(test_data))
    test_data = data_transforms['test'](transforms.ToPILImage()(test_data))
    test_data = test_data.cuda()
    test_target = torch.tensor(test_target)
    test_target = test_target.cuda()
    test_data.unsqueeze_(0)
    test_target.unsqueeze_(0)
    print(test_data.shape)
    output = model_ft(test_data)
    pred = torch.argmax(output, 1)
    loocv_preds.append(pred)
    loocv_targets.append(test_target.item())


print("loocv preds: ", loocv_preds)
print("loocv targets: ", loocv_targets)
print(accuracy_score(loocv_targets, loocv_preds))
print(confusion_matrix(loocv_targets, loocv_preds))