I am trying to classify around 400K data with 13 attributes. I have used python sklearn's SVM package, but it didn't work, and then I learned that SVM's are not suitable for large dataset classification. Then I used the (sklearn) ANN using the following MLPClassifier:
MLPClassifier(solver='adam', alpha=1e-5, random_state=1,activation='relu', max_iter=500)
and trained the system using 200K samples, and tested the model on the remaining ones. The classification worked well. However, my concern is that the system is over trained or overfit. Can you please guide me on the number of hidden layers and node sizes to make sure that there is no overfit? (I have learned that the default implementation has 100 hidden neurons. Is it ok to use the default implementation as is?)
To know if your are overfitting you have to compute:
Training set accuracy
Test set accuracy
Once you have calculated this scores, compare it. If training set score is much better than your test set score, then you are overfitting. This means that your model is "memorizing" your data, instead of learning from it to make future predictions.
If you are overfitting with Neuronal Networks you probably have to reduce the number of layers and reduce the number of neurons per layer. There isn't any strict rule that says the number of layer or neurons you need depending on you dataset size. Every dataset can behaves completely different with the same dataset size.
So, to conclude, if you are overfitting, you would have to evaluate your model accuracy using different parameters of layers and number of neurons, and, then, observe with which values you obtain the best results. There are some methods you can use to find the best parameters, is like gridsearchCV.
Related
I'm trying to train a multilabel text classification model using BERT. Each piece of text can belong to 0 or more of a total of 485 classes. My model consists of a dropout layer and a linear layer added on top of the pooled output from the bert-base-uncased model from Hugging Face. The loss function I'm using is the BCEWithLogitsLoss in PyTorch.
I have millions of labeled observations to train on. But the training data are highly unbalanced, with some labels appearing in less than 10 observations and others appearing in more than 100K observations! I'd like to get a "good" recall.
My first attempt at training without adjusting for data imbalance produced a micro recall rate of 70% (good enough) but a macro recall rate of 45% (not good enough). These numbers indicate that the model isn't performing well on underrepresented classes.
How can I effectively adjust for the data imbalance during training to improve the macro recall rate? I see we can provide label weights to BCEWithLogitsLoss loss function. But given the very high imbalance in my data leading to weights in the range of 1 to 1M, can I actually get the model to converge? My initial experiments show that a weighted loss function is going up and down during training.
Alternatively, is there a better approach than using BERT + dropout + linear layer for this type of task?
In your case it might be helpful to balance the labels in the training data. You have a lot of data, so you could afford to loose a part of it by balancing. But before you do this, I recommend to read this answer about balancing classes in traing data.
If you really only care about recall, you could try to tune your model maximizing recall.
I builted some network based on LSTM. I tuneded parameters. The results are shown in the figure and are not impressive.
How to understand what is bad? Is the dataset bad or the network is not well built?
Since validation loss decreased initially and later increased what you're experiencing is model overfitting.
Since training loss kept decreasing, your model has learnt training set excessively and now model is not generalizing well. Due to this validation loss increased.
To avoid overfitting, you need to regularize your model. You can use L1 or L2 regularization techniques. Additionally, you can also try dropout in your model.
Now coming to your question:
If the dataset is of good quality i.e. it is annotated well and it surely has features which could give result, then dataset and model hand-in-hand decides the quality of the predictions.
Since you're using RNNs that consists a good numbers of parameters, make sure that dataset is also huge to avoid RNNs overfitting on a small dataset. If available dataset is small, start with a small deep learning with less parameters (you can build a small neural network) and gradually scale up the model until you're satisfied with the prediction scores.
You can also refer this: https://towardsdatascience.com/rnn-training-tips-and-tricks-2bf687e67527
I have trained a model and it took me quite a while to find the correct hyperparameters.
The model has now been trained for 15h and it seems to to its job quite well.
When I observed the training and validation loss though, the training loss is somewhat higher than the validation loss. (red curve: training, green: validation)
I use dropout to regularize my model and as far as I have understood, droput is is only applied during training which might be the reason.
Now Iam wondering if I have trained a valid model?
It doesn't seem like the model is heavily underfitted?
Thanks in advance for any advice,
cheers,
M
First, check whether you have good data set, i.e., if it is a classification, then get equal number of images for all classes and get it from same source not from different sources. And regularization, dropout are used for overfitting/High variance so don't worry about these.
Then, I think your model is doing good when you trained your model the initial error between them are different but as you increased the epochs then they both got into some steady path. So it is good. And may be reason for this is as I mentioned above or you should try shuffle them then using train_test_split for getting better distribution of training and validation sets.
A plot of learning curves shows a good fit if:
The plot of training loss decreases to a point of stability.
The plot of validation loss decreases to a point of stability and has a small gap with the training loss.
In your case these conditions are satisfied.
Still if you want to deal with High Bias/underfitting then here are few methods:
Train bigger models
Train longer. Use better optimization techniques
Try different Neural Network Architecture and also hyper parameters
And also you can use cross-validation or GridSearchCV for finding better optimizer or hyper parameters but it may take really long because you have to train it on different parameters each time considering your time which is 15 hours then it might be very long but you will find better parameters and then train on it.
Above all I think your model is doing okay.
If your model underfits, its performance will be lower, similar as in the case of overfitting, because actually it can not learn effectively to get the optimal result, i.e the proper function to fit the given distribution. So you have to use less regularization technique e.g. less dropout to get the optimal result.
Furthermore the sampling can also be crucial, because there can be training-validation subsets where your model performs well on validation set and less effective on training set and vice-versa. This is one of the reason why we use crossvalidation and different sampling methods e.g. stratified k-fold.
I have a machine learning model built that tries to predict weather data, and in this case I am doing a prediction on whether or not it will rain tomorrow (a binary prediction of Yes/No).
In the dataset there is about 50 input variables, and I have 65,000 entries in the dataset.
I am currently running a RNN with a single hidden layer, with 35 nodes in the hidden layer. I am using PyTorch's NLLLoss as my loss function, and Adaboost for the optimization function. I've tried many different learning rates, and 0.01 seems to be working fairly well.
After running for 150 epochs, I notice that I start to converge around .80 accuracy for my test data. However, I would wish for this to be even higher. However, it seems like the model is stuck oscillating around some sort of saddle or local minimum. (A graph of this is below)
What are the most effective ways to get out of this "valley" that the model seems to be stuck in?
Not sure why exactly you are using only one hidden layer and what is the shape of your history data but here are the things you can try:
Try more than one hidden layer
Experiment with LSTM and GRU layer and combination of these layers together with RNN.
Shape of your data i.e. the history you look at to predict the weather.
Make sure your features are scaled properly since you have about 50 input variables.
Your question is little ambiguous as you mentioned RNN with a single hidden layer. Also without knowing the entire neural network architecture, it is tough to say how can you bring in improvements. So, I would like to add a few points.
You mentioned that you are using "Adaboost" as the optimization function but PyTorch doesn't have any such optimizer. Did you try using SGD or Adam optimizers which are very useful?
Do you have any regularization term in the loss function? Are you familiar with dropout? Did you check the training performance? Does your model overfit?
Do you have a baseline model/algorithm so that you can compare whether 80% accuracy is good or not?
150 epochs just for a binary classification task looks too much. Why don't you start from an off-the-shelf classifier model? You can find several examples of regression, classification in this tutorial.
I am using sklearn's random forests module to predict values based on 50 different dimensions. When I increase the number of dimensions to 150, the accuracy of the model decreases dramatically. I would expect more data to only make the model more accurate, but more features tend to make the model less accurate.
I suspect that splitting might only be done across one dimension which means that features which are actually more important get less attention when building trees. Could this be the reason?
Yes, the additional features you have added might not have good predictive power and as random forest takes random subset of features to build individual trees, the original 50 features might have got missed out. To test this hypothesis, you can plot variable importance using sklearn.
Your model is overfitting the data.
From Wikipedia:
An overfitted model is a statistical model that contains more parameters than can be justified by the data.
https://qph.fs.quoracdn.net/main-qimg-412c8556aacf7e25b86bba63e9e67ac6-c
There are plenty of illustrations of overfitting, but for instance, this 2d plot represents the different functions that would have been learned for a binary classification task. Because the function on the right has too many parameters, it learns wrongs data patterns that don't generalize properly.