How to train pytorch model with numpy data and batch size?
I am learning the basics of pytorch and thought to create a simple 4 layer nerual network with dropout to train IRIS dataset for classification. After refering to many tutorials I wrote this code.

import pandas as pd
from sklearn.datasets import load_iris
import torch
from torch.autograd import Variable

epochs=300
batch_size=20
lr=0.01

#loading data as numpy array
data = load_iris()
X=data.data
y=pd.get_dummies(data.target).values

#convert to tensor
X= Variable(torch.from_numpy(X), requires_grad=False)
y=Variable(torch.from_numpy(y), requires_grad=False)
print(X.size(),y.size())

#neural net model
model = torch.nn.Sequential(
    torch.nn.Linear(4, 10),
    torch.nn.ReLU(),
    torch.nn.Dropout(),
    torch.nn.Linear(10, 5),
    torch.nn.ReLU(),
    torch.nn.Dropout(),
    torch.nn.Linear(5, 3),
    torch.nn.Softmax()
)

print(model)

# Loss and Optimizer
optimizer = torch.optim.Adam(model.parameters(), lr=lr)  
loss_func = torch.nn.CrossEntropyLoss()  

for i in range(epochs):
    # Forward pass
    y_pred = model(X)

    # Compute and print loss.
    loss = loss_func(y_pred, y)
    print(i, loss.data[0])

    # Before the backward pass, use the optimizer object to zero all of the
    # gradients for the variables it will update (which are the learnable weights
    # of the model)
    optimizer.zero_grad()

    # Backward pass
    loss.backward()

    # Calling the step function on an Optimizer makes an update to its parameters
    optimizer.step()


There are currently two problems I am facing.


I want to set a batch size of 20. How should I do this?
At this step y_pred = model(X) its showing this error


Error

 TypeError: addmm_ received an invalid combination of arguments - got (int, int, torch.DoubleTensor, torch.FloatTensor), but expected one of:
 * (torch.DoubleTensor mat1, torch.DoubleTensor mat2)
 * (torch.SparseDoubleTensor mat1, torch.DoubleTensor mat2)
 * (float beta, torch.DoubleTensor mat1, torch.DoubleTensor mat2)
 * (float alpha, torch.DoubleTensor mat1, torch.DoubleTensor mat2)
 * (float beta, torch.SparseDoubleTensor mat1, torch.DoubleTensor mat2)
 * (float alpha, torch.SparseDoubleTensor mat1, torch.DoubleTensor mat2)
 * (float beta, float alpha, torch.DoubleTensor mat1, torch.DoubleTensor mat2)
      didn't match because some of the arguments have invalid types: (int, int, torch.DoubleTensor, !torch.FloatTensor!)
 * (float beta, float alpha, torch.SparseDoubleTensor mat1, torch.DoubleTensor mat2)
      didn't match because some of the arguments have invalid types: (int, int, !torch.DoubleTensor!, !torch.FloatTensor!)



  I want to set a batch size of 20. How should I do this?


For data processing and loading, PyTorch provide two classes, one is Dataset, which is used to represent your dataset. Specifically, Dataset provide the interface to get one sample from the whole dataset using the sample index. 

But Dataset is not enough, for large dataset, we need to do batch processing. So PyTorch provide a second class Dataloader, which is used to generate batches from the Dataset given the batch size and other parameters. 

For your specific case, I think you should try TensorDataset. Then use a Dataloader to set batch size to 20. Just look through the PyTorch official examples to get a sense how to do it.


  At this step y_pred = model(X) its showing this error


The error message is pretty informative. Your input X to the model is type DoubleTensor. But your model parameters have type FloatTensor. In PyTorch, you can not do operation between Tensors of different types. What you should do is replace the line

X= Variable(torch.from_numpy(X), requires_grad=False)


with 

X= Variable(torch.from_numpy(X).float(), requires_grad=False)


Now, X has type FloatTensor, the error message should disappear.

Also, as a gentle reminder, there are pretty much materials on the Internet about your question which can sufficiently solve your problem. You should try hard to solve it by yourself.
